Need to replace my Ft. Struts on my 87 109D 2.5 and saw 3 choices for replacements. A Standard, an Heavy Duty and a Sport. Anyone know the difference? (gonna do the rears as well) I am hoping to get a much firmer ride and I think that MB had HD for Taxi service...Are they interchangable or would I have to change pads etc. to go from std to the HD or Sport? Thanks! Clip