RSM is rear shock mount located at the top of the rear shocks
well the 5th gear issue is not really serious i believe it's just a broken or loose pin in the tranny.. until the tranny is hot it will stick there. but after it's hot it will be back to normal. The only bad thing about the 5th gear thing is that if you mistakenly shift to something you don't want to be shifting in hehe AKA "Miss-shift" then you'll have a very expensive blown engine. I suggest that you try to fine something that doesn't have that issue.
Also, when I looked around for my M Coupe I checked a couple of M Roadster's and e36 M3's most of them doesn't have the issue so I guess the 5th gear issue is not rampant.
PS: Oppps posted on my dad's account.. its me crusher