Jon Goodman has been the go to person for light seal replacement kits for ages but I don'y know if he is still doing them, try emailing him at
jon_goodman@yahoo.com. I use 1.0mm foam on my Ricoh 550G camera and I understand that the 500ME uses the same and it is widely available on the 'net, a sheet of 7x5in cost me £4. The seals are easily replaced, albeit a bitt messy to remove the old ones, There are vidoes on the 'net showing how to carry out the replacement and if you can use a ruler and craft knife you should have no problem.