The distributor really doesn't use a seal as it turns in the hole - providing the vacuum advance is working. There are two groves on the upper part of the distributor where it goes in to the block. You could pull the distributor and put some silicone in the upper groove, this may slow down the leak. You just don't want to stop it from turning.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine