I treat all my leather items, what's one more.
Tell the camel that is is only one more straw.
Hey, I like leather a lot. But, constant exposure to the elements makes it break down far sooner than plastic that is UV protected. If the bike spends more time out of the weather than in it, AND is treated regularly with moisturizers, and water proofing products, it can have a decent service life. I speculate that human skin oils do approximate the cows secretions to keep the leather supple. Perhaps riding with buttless chaps is a good technique for extending the life of leather seats?
However, water, oxygen, and bacteria are natural breakdown agents used to return the cow's hide to mother earth's recyclable nutrients. Not many prehistoric cowhides are still in existence, I note.
The problem both vinyl and leather is that it is punctured during assembly, which lets water pass through the membrane at the puncture points, getting to foam and metal pan.
You'll note that the stock seat vinyl components were bonded/embossed with heat, fusing the plastic together forming a water shedding canopy over the seat foam and pan. This is why a sheet of plastic is put between the cover and vinyl replacement covers, imo. I think that treating all stitching with RTV, might approximate the bonded, heat fused method. However, Vinyl often has a mold release agent applied to it during manufacture, which would interfere with the RTV bond. So, planing ahead and cleaning all stitching paths before assembly would also be required. Labor intensive and expensive to do it right, I expect.
Do use marine vinyl over other types of vinyl, as that is the only vinyl that won't harden and crack with more than 5 years of exposure to the sun.
