There are products that claim to do this- the one that is heard of most is by Lucas. Also a blue devil or some such. You need to carefully examine how these work to avoid more trouble. The most common type is a rubber conditioner, most effective for old seals which have been sitting for a while. For new rope seals it isn't going to do anything for you. There are others that will close up small passages- this has some obvious potential problems for sealing things you don't want sealed. The most likely approach for your situation are products that will initiate a seal if they encounter air on the other side of a small passage. This approach has some success for transmissions, and may work for engines as well. So you need to find out how a product is supposed to work before trying.
