1997+ #5 spring pad exists?
 

Or can i use the front #5 since the other pads are the same parts number?

This is for the rear spring.

For W202 mid 96-99
Front(W210 part number) :
210 321 01 84 pad#1 5 mm
210 321 02 84 pad#2 9 mm
210 321 03 84 pad#3 13 mm
210 321 04 84 pad#4 17 mm
210 321 05 84 pad#5 21 mm

Rear(W210 part number) :
210 325 01 84 pad#1 5 mm
210 325 02 84 pad#2 9 mm
210 325 03 84 pad#3 13 mm
210 325 04 84 pad#4 17 mm