The original owner of my boat forgot and left a rubber piece sitting in the front seat over the winter and it left a stain on the bow seat. Any suggestions on what might remove it. I have tried tilex and WD-40. They didn't work. I was going to try a bleech mix or some comet.

....try wd 40 and magic eraser together

comet with a little water works great...we use it on a lot of our trade-ins if needed.

Magic Erasers and Starbrite vinyl cleaner work well for me, but I've found that the best way to get the stain out of vinyl is letting it sit in the sun. I used to get all stressed about the occasional small stains in my vinyl, but after owning 2 boats now with a third on the way, I've learned that they will eventually go away after a few times out....

+1 for the sun. If the magic eraser wd40 or Starbrite doesn't work, be patient and see what the sun will do for it. I have also had success with an ammonia/peroxide mixture.

10% benzoil perxoide ( acne medication), and let it sit in the sun, then wash off.