You dunk the seals in mineral spirits then install them very very quickly. Once the mineral spirits touches the seals, the seals begin to expand VERY quickly. That's why you give them a quick dunk and get them in. Wait around too long and the seals will expand so big that you can't get them in with the main seal cap.

Never thought to hit them with mineral spirits after the fact but I guess it should work. I think last time I used paint thinner instead of mineral spirits and it worked the same.