The 45 transitioned to synthetic seals in 1984 or thereabouts. Look on the left rear of the receiver. You should see four tiny numbers as in 04 87. That's the month/year it was made.
Leather seals are not a problem. If it's a pre-1984 gun and shooting a bit weakly, just put a few drops of pure silicone oil (try a hobby shop) down the transfer port where the air comes out and stand the rifle on its butt for a couple of days to let it soak in. This often rejuvenates a dry seal. The synthetic seal may give you a bit more fps. And I think Jim Maccari offers a synthetic replacement should your leather seal be beyond redemption. 45's of your vintage are very nice guns.
