http://www.thisoldtractor.com/gtbender/
Updated: 2010 Mar 23
I recently replaced my original spark plug cap with an NGK VD05FP (8429). Has the waterproof covers. Fits and works a treat. I've a 1993 DR350. You'll want to check the specifications to make sure it works with the later spark plugs, etc. Here is a great document from NGK that will tell you about each resistor cover (as they call them).