Rear main seal - today's best sealant?
 

Can't seem to get a M103 rear main seal to last more than 4-5 years. Bummer.
I really think the leak occurs around the seal cover/block interface, not the seal ring.
I have always used Permatex black. Maybe not the best thing?
I also use Permatex black on the front timing cover, and it also lasts about 5 years.

Did a thorough search on the sealants, but still confused.
The cover is metal-to-metal, so may need an aneorobic sealant?
But the base of the cover rests on the pan gasket, so needs a conventional gasket sealant to mate there?

The M103 book says 001 989 45 20 10, but that's probably been discontinued for 20 years.

Gurus here recommend Loctite 5900, which I think is aneorobic - but I have had zero luck finding it, except maybe by the case for $300.

Others say the new Hylomar formulations are good, or the current MB 003 989 98 20 10; but I can't find out much about it (except it's $$$$).

Any thoughts?? - don't want to do this again for awhile.

Tks,
DG

If you have been using an rtv based sealer that is your problem. It should be an anaerobic type. Also hopefully you have not been using anything aggressive to clean the aluminum "housing". I use loctite brand "case sealer" on all my stuff. I have a tube on my bench at work, can't think of the number for the life of me at present. I will look tomorrow and forward it to you. Also clean is the thing, I wipe everything down with laquer thinner prior to assy.

ps--if the mating surfaces are out of whack, you can dress them up on a piece of 400 wet/dry (wet) on a piece of glass...

What is an example of a common anaerobic type?

sealant
 

you may want to try the black sealant from mercedes benz. It comes in a white plastic tube and comes with funnel type tip and black plastic tube pusher tool.

DG, I second the MB black sealant. Used it when doing the upper timing chain cover on a 104 engine and had no more oil leakage. Be sure to get the mating surfaces super clean,true and dry before application.

Just make sure the M-B sealant is fresh. It has a shelf life of one year and will get very hard to squeeze out of the tube after that. The tube is dated.

What I've been using: Loctite 574

Thanks guys. Yeah, I think the MB 003 989 98 20 10 I posted above is the black stuff you mentioned. I'm not for sure it's an aneorobic, but it says it's for metal-metal use, which would indicate it is.
One issue I have with using aneorobic sealant is: it will not bridge a gap of more than about 0.010 or so, and the interface with the oil pan gasket/block is pretty large - just about the same scenario as the upper timing cover where it joins the head gasket.

So, will the aneorobic work in the "cracks" along the pan gasket/block interface, or should I dab a little RTV stuff in there?

Tks,
DG

p.s. I may need to retire 'Ol Pearl due to old age - not her's, but mine!
I was sealing up the timing cover last week, and decided to install the cover, then press the radial cam seal in (touchy but doable).
I knocked the old seal out on the bench, did a great job of installing the cover; and then grabbed the radial seal, and it went in soooo easy and smooth!
Danced around the garage celebrating, then walked over and FOUND THE NEW SEAL STILL LYING ON THE WORKBENCH. Oh, well, it finally all ended well.

Just to follow up, I checked with the local dealership tech, and he recommended the MB silicon sealant 003 989 98 2010, also apparantly known as Reinzosil. Obviously not anerobic, but at least it eliminates my worries about how an anerobic would handle the pan gasket interface.

I'll let you know how it worked in about 5 years - I hope.

DG

Sealers
 

Loctite 574 IS one of their Anorobic sealants (Mercedes Timing Cover)
[The 574 also has a separate Mercedes Part # (and Price) ]

I used some Mercedes orange sealant MB No. 002 989 00 20 10 on the front covers of my 400E and it was $55 ten years ago. It was really good stuff. I wouldn't mind having another tube of that if I could get it for a reasonable price.

Doesn't success depend on proper prep and application? If so it would stand to reason that anything designed to do the job should work admirably. A lot of people don't like the idea of an RTV silicone type sealant because sometimes it breaks loose on the inside and clogs oil passages.

Permatex aviation is one example of an anaerobic sealant.

For sealing metal to metal, something like Threebond 1104 should work great as that's what I've used on motorcycle cases which in my limited experience are rarely perfectly machined and are subject to high temps and vibration. Never had a leak because that stuff is awesome. It's quite popular with the Porsche crowd. I probably wouldn't use just any old Permatex RTV they sell at McParts though. Can't go wrong with whatever MB uses.

I'd say if you clean the mating surfaces like you're supposed to and apply the goop in a nice neat bead you should not have any issues but there's a great potential for error there as common definitions of clean and neat vary wildly.

Well, I'm definitely on the lunatic fringe end of clean/neat, so that's no problem. And i agree, it's like good paint jobs, prep is 90%. Really my biggest concern was how the aneorobic would interface with the big cracks at the pan gasket/block/pan interface, and along the gasket surface - a similar issue with the front cover gasket where a dab of silicone is specified. Globing on some silicone, and intermixing with the aneorobic at this interface sounds less than optimal for good adhesion of both types.
back 30 years ago, we used Yamabond aneorobic sealant to join the machined cases of motorcycles and it worked great; didn't ooze at all, and left a very thin uniform layer on the junction when you pulled the cases apart next time.

DG

Yamabond is Threebond 1104, also known as Hondabond, Ducatibond, etc. Excellent stuff. I think you should try it on your car.

1104 has been replaced with 1194 as 1104 contained lead which has been banned. However you can still get 1104 if you look around. I got a tube recently from an online Ducati guru in FL. I've heard there's not much difference, 1104 being only slightly preferred over the new stuff.

If it's good enough to seal the case halves on a flat six it should work on your much smoother M103.

Ha, I went through my old box of chemicals last week and found a 40-yr-old tube of Yamabond 4. It actually still felt pliable inside the metal tube - but the label said use within one year. So, I reluctently tossed it, along with some 1970 Hodaka shifter springs.

Now, as luck has a way of doing, while waiting for better weather to do the rear main, I am seeing a developing oil leak from the head gasket! I guess it's time, it's been about 10 years and 100k. Well, my January dance card just got filled.

Cheers,
DG