I probably know this answer before I ask it, but will give it a try anyway.

Can the plastic fenders be reconditioned somehow, or do you have to find new or used to replace them?

My 19 year old TRX300 is in excellent condition with the exception of the plastic.
It has faded and been scratched throughout the years. Nothing is torn or broken.

If replacement is the only option, what years will replace my 1989 TRX 300? Will any mods be required?

 

You could try using a heat gun from lowes. I used them when detailing cars. Worked great for slightly melting the black molding and making them look black again. Might work great for fenders.......

 

Try some Plexus plastic polish.

 

There are various plastic buffing kits out on the market. They work well if you take your time.

PC Racing makes a product called plastic renew. I haven't used it, but it might be worth a shot.

 

yeah the PC racing plastic renew is supposed to work. i haven't used it myself either but i read a review on it in QUAD magazine and they said it works really well. The only downfall about it though is that they said it takes a while and a lot of elbow grease to really clean up your plastic.

 

my brother used the plastic renew on his raptor and it took out the scraches because you have to sand paper the plastic 3 to 4 times then you put the finish on it, and that is what takes a long time.

 

PC plastic renew works awesome, I used it anout a week ago on my 400EX, you sand it first with rough 220 grit, then 320 grit, then 400grit, then you use steel wool, then you apply a coat of liquid it includes for you, let it dry, then repeat applying the liquid for four or five times, letting it dry each time, it will get brighter and brighter every time, works great for faded plastic