I had the same issue as most with my "14" Z118C. The bolsters were fading and looking stained (white streaks) from I assume water. My boat is gargaed so the only sun it sees is when I am fishing and that is not as much as most. Anything I tried to bring back color was only temporary at best so I decided to paint them with a spray paint rated for plastic.
I was going to remove the seats anyway to clean behind them and removed the bolsters. There is your pretty finish behind them whatever color or finishg you have so it would look good with out them. Some screw holes would have to be dealt with and probably some non skid on the ramp and down by where the reels ride to prevent scratching of gel coat.
There is some old contact cement to remove where carpet is covering screw heads. Don't worry, that plastic is some tough stuff and acetone does not even phase it.
I sprayed mine with flat black and cut some new pieces of carpet. Re-installed and cemented carpet pieces last and at least for now, looks good as new. Time will tell.
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