SLS Valve, Pump, accumulator woes? 1979 300TD

[79greaser]

So,
I have read several threads regarding SLS and have come to the conclusion that I am in for a few hundred dollars in repairs. Here are my symptoms.
Symptoms
1. The car losses it's level over night. It sets down the rear to just lower than level after sitting for a day or so. When I start it up, I can feel (see in the rear-view) the car lift.
2. The ride is pretty good until I hit a pot hole, then it feels like it comes down really "hard"
3. Lately I have come out to an overflowed hydraulic reservoir which looks like it has bubbly motor oil in it. This happens when I turn the car off even for a short while (5min).

Fix?
The parts for this system add up quickly. I don't want to do anything twice, but would like to get away without replacing everything at once. Am I right to think that I MUST replace the pump seals, valve seals, and 2 new accumulators? I have not come across a good how to on the pump rebuild and am wondering how I can check my springs and buffers when I am under there? There are 3 buffer sizes and am not sure how to measure the correct rear end height to see if I need these as well. What else should I be checking now that I am going to get in this far? Any help on the matter would be appreciated.

[Carpenterman]

Overnight sagging is almost always a leaking valve. A member over on the Diesel Forum sells a rebuild kit for about $10 and somewhere on that same forum is a DIY for the rebuild. Do some searches over there and I'm sure you'll find what you need. A rebuild fixed my sagging rear end.

I would rebuild the valve and while the system was open, check the accumulators by removing the longitudinal fitting and inserting a small rod such as a pencil into the cavity. If it doesn't meet any resistance and goes all the way in, they are shot. If yours are original, they have almost certainly failed. I'm not sure what you mean by "bottoming hard", but failed accumulators usually result in a hard bouncy ride. New accumulators made my wagon ride like a different car.

In the hundreds of posts I've read from TD owners I have never heard of a pump failing and don't know if they are rebuildable. The actuators (hydraulic shocks) are also pretty robust and not prone to failure.

As far as height goes, guys usually measure to the side body moulding from the ground at the front and back to check for proper height. Your springs may be a little tired after all these years, but you could also change your height by adjusting the arm on the valve.

[79greaser]

Thanks Carpenterman,
It just seems to come down like a rock when I hit a pothole, Just very hard. no crazy noises or anything, just hard. I have new accumulators, a valve rebuild, and a pump seal kit coming next week. I am going to tackle the SlS valve removal this weekend. I was going to skip resealing the pump, and hope that my fluid was just "dirty" but fear I may have a bad seal in my pump too since the color is so dark and looks like oil is getting in. All said I'm in $90 for the valve (dealer), $206 for accumulators (********) and another $75 for fluid and a filter. A bit pricey, but I only want to work on this system once if possible. A lot of good links over there on the diesel forum. Thanks for your advice.

[mercmad6.3]

The lip seal on the rear of the pump has gone and it's sucking engine oil into the suspension oil.

You need to clean out the suspension by disconnecting the shocks from the spheres and pushing them up so the oil comes out ,replacing your failed spheres ( new hoses are good idea if engine oil has gotten in there. )
Remove the reservoir and wash it out and replace the filter and low pressure return line .
I find it better to disconnect the pipes for the suspension and blow air down the pipes to get the worst of the engine oil out.
Your rear valve has failed so repair that and replace the link rod too,the ball ends will be worn by now.
When you have the spheres,hoses and the pump back on the block,fill the reservoir with new SLS fluid (NOT hydraulic oil,auto trans fluid ,Citroen HS oil or brake fluid...) and bleed the high pressure line by aiming it from the pump into the reservoir until it runs clear.it takes a few seconds to do this but if you dont because it seems liker too much work,the pump will fail again.
Reconnect it to the pump and sit the car on it's rear wheels. Load the rear with 100kgs of weight ( I fill four 25 liter buckets with water) and with the engine idling and a hose connected to the rear valves bleed nipple,let the pump run oil through the valve until all air is ejected. The back should rise to it's full level and remain there once the valve is tightened up. Check for leaks etc.
The lower ball joints on the rear hydro shocks can wear out so if the shocks are oily and you hear clunking sounds from the rear,the shocks need replacing. Same story,load the rear up and bleed the suspension .
The oil from the bleed process can be used again,just stick it back in your reservoir.
In future,anytime the fluid looks dirty,it's a clear sign you have a problem that needs attention. It should remain clear all the time.