rear main seal leaking

[Ricko1937]

I am restoring a 1934 Chrysler 6 cyl. 241ci engine. The engine is in the car and running. I have had problems with the rear main seal leaking while running. I relaced with a second one and it leaks worse. These seals are the type that bolt to the rear of the block with a flush mount. The are not grooved into the block. It is also the vulcanized hard rubber and not the rope type. I thought it may have been the hardness of the rubber causing my problem but my 2nd seal was much softer. I think these seals may have dried up over the years and was wondering if anyting could be used to sweel the rubber. Any help would be appreciated.