You might want to get a power valve tester to see if yours is really blown:
http://www.jegs.com/cgi-bin/ncommerc...61&prmenbr=361
You'll also need a hand vacuum pump with a reasonably accurate gauge.
I know it's a bit pricey, buying a $32 tool to check a $5 part. However, it's nice to be able to check out the fault to see if it's actually a fault, rather than just changing parts and hoping. My 2 cents, FWIW.