Mendi

Seats/covers would be hard to find from other than an OEM, unless you find someone who has bought a dealer stock that has stopped selling the boat lineup. I chose to re-cover my own, but they are different from your pedestal seating.
Best bet there is your local upholstery shop, or try eBay for odd parts. Decals are inexpensive, unless you're looking for the larger ones. The stereo can be replaced with any marine grade unit, try www.overtons.com or www.westmarine.com .
The original Seadoo boat covers are not cheap, either, and those, too, can be found on eBay at times.
I'm sure you have tried cleaning the marks on the seats. If not, try 3M Marine Vinyl Cleaner.
Check out our links page for places to buy OEM parts.

Thank you for your reply. Since the overall interior/exterior of my '99 1800 is like new as it sat on trailer for 2 1/2 years with less than 50 hrs. on orig engines, I do have access to cushions, a faded sunlounge decal, from my local dealer. Will have in their shop soon for old oil/gas removal, full mechanical ck out, ect. Seadoo has parts & recommended since I will be paying dearly for shop work, I should be able to get some discounts on the items I want to replace on boat. The pedistal seats are unique to this boat, but the 4 ea. cushions are pricey.