I think the '96 W210 cars use infrared remote locking - there is only one sensor and it sprouts out the bottom of the rear view mirror.
RE getting a new key to work; the owners manual tells how to re-synchronize the key. If you don't have your manual, let me know I'll read mine for you. Or (your best bet) try the search.
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