I agree and disagree Coot. From what I understand, all Synthetic oils swell seals a little. Most seal swell products, keep swelling to the point of destroying the seal, the trans fluid and the Malco product will only swell to a certain point then stop. I think the best product for rejuvenating rubber is linseed oil, works great on exterior rubber, I've never used it for seals except for front bearing hub on my four by.