The RH forward rear shock absorber is leaking, and will need to be replaced. I can get a Boge from the UK for 70-80 quid including postage, which is distinctly cheaper than getting it from Japan, but am wondering if all four rears should be replaced at the same time. In other words, is just one new shock likely to affect the ride? Or am I overthinking the issue?
(I want to keep her stock - I don't want a firmer ride: she's already rather more sensitive to bad roads than I hoped.)

 

Ideally you'd replace them in pairs on each side, but you could probably get away with one. It's a shaft through both on the bottom, and bolts at the top. Not much more work to take off 2 as one.

The spring will need to be compressed and removed to replace the shock, so a bit more work to do both.

 

I would be inclined to all 4 and be done with it.

For spring compressor I used the rear disk rotors as they were off the car, the regular spring compressors you buy at the auto shop will not work.

 

Thanks muchly, as always, Jagboi and Warrjon. One vote for two, one vote for four.
I like your spring compressors, Warrjon. However, I won't be doing the actual work myself, but it will be done along with fixing the leaking diff, which is leaking oil from where the driveshaft goes in.
I wonder if I should get them to inspect the inboard rear brakes while they're in there, or is that accessed separately?

 

Is there a generic part number or size spec for XJS shocks that somebody has handy? I've been looking at brands etc I want a particular type however they specialize in truck/jeep aftermarket so I'd need to see if some of the options could fit.

 

Doubtful, since the shock also carries the spring, unlike most cars. The shock and spring come off the car as an assembly.

 

Ideally, all 4. You could probably get away with just doing 2 if funds are tight. So call it 1.5 votes for 4, 0.5 votes for 2!

They will be right next to the brakes, all there really is to inspect is rotor thickness (minimum is 0.45", new is 0.5"). They typically are long lived though. Pads do wear, get them to have a look at how much remains while they have it on the hoist.

If they are changing the pinion seal it is absolutely vital to return the pinion nut to exactly the same position it was before, as this controls the preload on the pinion bearings and the backlash between the pinion and crown gears. Ideally punch a reference mark on each component (pinion gear shaft, nut and flange) and line every thing up before and after disassembly.

The nut is very tight, expect torques in the range of 130-150 ft-lbs. You'll need an adapter to bolt to the driveshaft flange to hold the pinion in place while torquing the nut. Also it has to be done slowly and carefully as you can't back off if you overtighten, as it over crushes the spacer sleeve that controls preload. If you do go too far the differential has to be taken apart and rebuilt. That's a big job! (been there, done it).

 

Vancouver: the rear shocks are part number CBC5742.
Jagboi: funds aren't particularly tight - that is, I'd prefer to get the job done right than done cheaply. So four it is.
Thanks for the warning about the pinion seal. I'll translate that and pass it on (I suspect they might know/be aware of such issues - this place deals with some very high end European cars - but you can't be too careful. Even if I do sometimes feel like I'm teaching my grandmother to suck eggs...).

 

One more thought is to have them put sealant on the splines between the flange and the pinion. Oil can leak through the splines, as well as past the sealing surface between the pinion and the seal.

 

Sealant on splines between flanges and pinion. Gotcha, and thanks again.

 

Here are some photos. The first shows the seal pressed into the housing. The shaft in the middle pointing up is the end of the pinion gear, the flange that bolts to the driveshaft fits on the splines of the shaft. Notice the gap between the seal lips and pinion? The flange sits in there and rides against the seal lips. However, the splines are not a perfect fit (you'd never be able to get it on or off if it was a fluid tight fit) so the oil can leak through the splines.

The second photo shows the IRS upside down and I included this photo to show the flange in place. The nut in the center is the one that the position is important. There is a washer and you can just smear sealant under the washer, but it also has to seal the threads.

You can see the shock/spring assemblies as well. It's a bolt at the top (bottom in the photo, since it's upside down) and shaft that goes through the radius arm to secure both of them on the lower side.
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Very helpful and clear. Thanks again, Jagboi. I'll print out the photos and take them along as well. It's definitely cheaper on a per-unit basis to get four shipped, so I'll do that, and once they're here, I'll get everything fixed up.

Incidentally, today marked One Year since my car arrived. Didn't really do anything special to commemorate, however. No cake or anything - though I did buy her some yummy engine oil....