So I have three cars I'm dealing with (two mine, one someone else's) that all have the same CV boot that went bad (two leaking, one ripped), the passenger's side inner. They're all the can style axles.
I haven't yet started working on them, but I thought I would ask about it before so I know better what I'm getting into.

Why is the same boot leaking on all three cars? Is it likely that there is a differential (pinion?) seal that is leaking? Or just some strange coincidence?

On the various Mercedes forums I have not read of any particular problem with the Passenger side inner Boots.

If the Differential Seals were leaking the Differential Oil Level will be lower.

The other way to tell is to degrease the Differential and go for a drive and see if you can detect where it is leaking from when you get back. However, if your Axle has emptied out all of the Oil it may not leak any more.

All of the Axle Boot replacement options has been well covered in the DIY Links.
Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/Wikka/DoItYourSelf

__________________
84 300D, 82 Volvo 244Gl Diesel

I figured it was just a strange coincidence.
On one of them the differential is pretty greasy so I'm going to try pressure washing it and checking the level of the fluid.
I'm guessing that one has a leaking seal somewhere.

I've looked through all the links. Think I have a good understanding of how to do the job.
Since this seems like a common problem and I'll be working on a lot of W123s I think I'm going to buy a gun and, if there's no diff leaks, do them with the axle still in the car to make it a lot quicker.

I'm guessing I should probably replace the axle with the split boot though? I don't know how long it was driven like that.
I'm selling the car so I might just get a low-miles used one and leave the boots stock

I just had the left inner let go...I jacked the back end of the car up and the stress of the joint flexing further than usual tore it completely open.

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

This is definitely a trend. Just came across a fourth car, an 81 300SD, that had the exact same boot ripped.
Is there some way that the differentials are geared that could cause higher vibration on this one boot?

__________________
New, Used & Rebuilt Parts for Classic Mercedes

mbzparts.com

The only difference on a 123 that I can see is that although the Exhaust Pipe starts out on the Passanger side by the time it is near the Differential it is over on the Drivers Side.
You would think that the extra Heat would make it more pron to cause a Driverside Boot problem but that does not seem to be the case.

__________________
84 300D, 82 Volvo 244Gl Diesel