I replaced one on my '96 (same body style as yours, W210) with a new from from Fastlane (click on link at top of page) It was only about $50 and it even came with all the bulbs! It was easy, pull away the trunk liner and you'll see three 10mm nuts and the one bolt with plastic clamp at the top. and it took all of a half hour (includes waxing the area exposed when the light is removed).
After you remove the old taillight assembly you may be able to repair it, I'd do that first.
Oh and don't torque the nuts down too much when you reinstall the assembly, you don't want to twist the housing and crack it.
RIP "Betsy" (Oo=*=oO)
'96 E 3 2 0 (W 2 1 0) M 1 0 4 (Totalled)
Spaces in sig so as not to screw up the SEARCH; every time someone searches for that MB they don't want my sig!
2004 Audi A8L
'98 VW Passat 1.8T 5M
'87 Alfa Romeo Milano 2.5L 5M
'67 Impala convertible, 327cid