Ugh, only 80K and the box is loose? Just did a quick search on www.car-part.com
(web based search engine for salvage yards) and see that you can buy a used box for your car for as little as 150 dollars. Might be worth considering. Don't normally hear folk complaining about the steering box in the W140s, so you may simply have a bad one... ?
If one of the techs has seen this before, I'd be curious to know. My '96 S500 Coupe has about 88K miles on it... is this another area to watch?
Anyway, had to smile when I read your comment on Jags... like you, I'm new to MB (got mine in January), but suffered through my "Jag experience" with a Series II XJ12L... folks that complain about MB reliability should try a 70s/80s Jag and see what British engineering is like... especially the Lucas systems, eh? Rebuilt the V12 and it was a work of engineering art (despite the leaks!) but the rest of the car was like a helicopter... for every hour you drove it, several hours of maintenance was necessary... :-) I understand they're much better since Ford bought them, but I'll never own another.
Good luck, keep us posted.
And, congrats on your beautiful W140 Coupe... !