Just to clarify -- my workaround was for the 4th gear OD switch on top of the gear case -- not the solenoid. The solenoid is quite easy to get to as it's on the bottom of the OD and near the back. All you need is a modified 25mm or 1" wrench or crow's foot. It's quite straight forward. And if you do need to remove the solenoid and don't want to drain the trans, jack the back end of the car up as high as possible to get as much fluid toward the front of the trans when you remove the solenoid. This will limit the fluid loss.

I think I mentioned in my other post that FCPGroton used to sell the synchros, but I don't see them on their website anymore. You might call them as they can do special orders for certain parts -- this may be one of them. What they had was probably SKF or ScanTech. I also checked with my dealer and the Volvo OEM stuff is $80 per synchro. I happened to have several dead gearboxes laying around, so I had a number of used ones to choose from. I did the first box several years ago with the Bentley manual and find that it's a fine digest for this service. There are 2 green books that cover the same thing. Biggest thing to remember is that the 3-4 gear selector ring has 3 teeth with slightly different beveling -- it's very subtle. The dogs go in there. If you don't line the dogs up properly when reassembling, you won't be able to shift.

When looking at used synchros, make sure that the teeth are not rounded and that there aren't deep grooves on each side (the teeth are triangular). You'll know what I mean when you look at them (it's from the synchros meshing with the gear teeth). Either can cause grinding. Also check the three slots on the inner ring where the dogs engage. If they are worn and misshapen (often you'll see that the slot has been elongated), the box either won't shift into the gear easily (synchros are not aligning the teeth properly) or it won't stay in gear (especially under deceleration). At least that's been my experience.

If you do the synchros, just give yourself plenty of time and keep a clean work surface. And be sure to bench-test the box before you put it back in the car. Better to fix a shifting problem now when it's easy to take it apart.

A depth gauge and calipers is handy for putting the shims back in. However, if you make sure that you keep everything in the same place (ie put the front intermediate shaft bearing race back in the front during reassembly), you shouldn't have too much trouble since you're not really changing the clearances.

Good luck. Cheers.