I bought a new set of front turn signal-to-body seals from PoP in Thailand. They installed easily and look great but when it came time to reinstall my lenses, I found rotted original inner seals. I bought a 12" x 12" square of 3 mm soft neoprene rubber from my local rubber supply house. I had an NOS seal as a pattern so after tracing out the original pattern on the new rubber, I used a metal ruler and a new razor blade to make the straight cuts, then followed up with a sharp pair of scissors for the corners. For the lens mounting hole, I used my electric drill and a 1/4" drill bit. Once the seal was ready and test fit, I applied a small amount of contact cement and glued the seal in place. Good as new!
<Update: March 2016: Unfortunately these seals are not available anymore, if you know where to find these, please let the moderator/forum know. >