Instead of constantly changing the rubber elements, you may want to
consider using a rubber cleaner/rejuvenator solution on them. My 4 year old
wipers still squeegee like brand new.
I use an industrial solution for transport systems in laser imagesetters
that contains a mixture of xylene,alcohol, ketone. There are similar
products available to the average consumer used on such things as rubber
rollers in copy/fax machines, or VCR capstan rollers. (Radio Shack used to
have it but I think they dropped it). Just look for rubber roller cleaner,
rubber rejuvenator, capstan roller cleaner. Stores and outlets that sell
supplies for electronic techs are likely to have it.
Also, cleaning rubber objects with plain isopropyl or ethyl alcohol may
seem like it helps in the short term, but repeated use actually lessens the
resiliency over the long term.
Of course, if the rubber is already so old and worn these rejuvenators may
not help. But using a solution on them 2 or 3 times a year will increase
the useful life tremendously.