When the petcock on my Bandit started leaking and "making oil" in the crankcase, I found the rubber diaphragm to be in virtually new condition, so I just stretched the original spring to get a little more closing force. That shortcut, of course, only lasted a couple of months, so I recently replaced the spring. For info, I found the Ace Hardware #6 compression spring, 5/16" OD, 1 1/2" length to work well after trimming to match the original spring length (approx. 3/4"). The replacement spring has a slightly smaller ID and slightly stronger spring rate (according to my calibrated thumb & index finger). Sharing this info for anyone who wants try just the 89¢ spring before using the full aftermarket rebuild kit. (Long post title is for search engine folks.)