Hi. I have a D2-55 on my 2005 39C. I replaced the air filter with a K & N cone type (similar to the one offered by Parts-4 Engines) about 8 years ago and it worked fine. You probably will never have to replace it ever again. Incidentally, I purchased engine parts from Parts-4 Engines in the past and was happy with what they supplied, and at a fraction of the price of VP original parts!
Regards,
Raph.