I have learned from my days of free flight that rubberbands last longer if they are "broken-in".
Just lubricate them with soapy solution and strecht them once for less than a minute.

I do it to my rubberbands and then I store them in a glass pot with soapy water.
I install them wet to attach the wings, and after use, I return them to the soapy solution, which takes care of the oil and where they stay until next use.

In this way, I discard them after several flying sessions, just to be safe, but I could say that at that point, they are as good as new.

Having clean fingers after I remove the bands from the wing is just a bonus.