Waddaya expect from Costco? They know Neons and K-cars.
The M102 1987 and up 130hp 2.3L 8V uses the spin-on filter (as above) and are readily available from your MB dealer. Try to find an indie mechanic that knows MB's if you are not going to change your own oil and hate the dealer's outrageous pricing.
Any Montreal area members know of someone trustworthy?
1998 C230 "Black Betty"