87 SDL rear end

Me again. Liesl is close to 100K. I suspect rear end issues:
* Shocks probably haven't been replaced
* She sits a bit low at back, empty
* Back wheels don't seem vertical - they're a tiny bit like so: / \
* 4 rubber booties on rear axles are starting to crumble
* Underside of car in diff area has grease/oil stains
* I sometimes hear a slight clunk during off-power shifts

What diagnostics can I do (i.e check gear oil level, drive shaft bushing). What shall I tell my shop to do? Note that she's getting a nice big car trip with fam/kids/luggage to Colorado in two months.

Thanks.