Man, 8.5 is nothing a couple coats of sealer won't fix, I've laid over wet slabs way worse than that and never had a callback. Testing is just two minutes of work that scares you out of jobs you could've taken.

How long did it take before you noticed a real difference with that cushion? I used to roll my eyes at guys dropping money on seat pads, figured it was just something to complain about online. Then my lower back started aching after every long day pouring concrete slabs and I got desperate enough to try one of those memory foam ones from a hardware store. It was not even close to the fancy stuff you see advertised, but man, the next morning I could actually bend over to tie my boots without wincing. Now I keep a spare in the truck for any machine with a worn out seat, since factory cushions are usually shot after a few thousand hours. Your mileage may vary depending on your height and how you sit, but for me it was night and day.