Unless you know for sure that the gasketing is totally shot (feel cold air escaping around the door/lid edge) then do the dollar bill test. If you put a dollar bill on the gasket and close the lid or door and can pull the bill out without __ANY__ resistance, it's time for new gasketing. If you're getting resistance, than you've got another issue besides the gasketing.
In terms of gasketing, I redid all mine last spring and it helped a huge amount. Ultimately I replaced the original Adler Barber unit but that's another story completely. I got the gasketing at Home Depot. Just ask for weather stripping 1/2 round gasketing. Worked like a charm.