Welcome! Sorry to hear you are having such problems.
Regarding the cost of the part, call Phil at the 800# for Partsshop (link at top of page) they can usually match anyone's price AND you support this site! They ship QUICK, too and have a wonderful returns policy (believe me I have used it enough)
Maybe you should try another brand of filter, I have faith in the Mann brand sold at Mercedesshop.com. Phil can order this for you too.
Good luck and keep us posted,
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