Hello David
Had some success using a product an automotive friend suggested. He gave me an 8 oz. bottle of AT-205 Re-Seal.
Used to rejuvenate seals, power steering, rack & pinion seals, transmission etc..
I used it to remove those rubber inserts for the PSU, soaked them, they came out pretty easy, softened them right up.
Liberally coated a 5 Point with it and it softened up the rubber significantly. Long term?? Will let you know.
Link to a random goggle search. Only difference is mine is blue and bilingual.
http://atpautomotive.com/featured/re-seal
Geoff