This applys to the exterior only - anybody have experience with the dreaded
break-down of the interior finish?  (I've fortunately not had to cross that
bridge as of yet.)

When browsing the fiber-glass product section of my local marine shop, I
noticed two types of products: those that were a cleaner/polisher, and those
that were just cleaners.  The cleaner-only were recommended for heavy
oxidization.

My pop-top was pretty bad, but I chose to try a cleaner/polisher (McGuires
[sic] Mirror Glaze - in a blue bottle) as it was noted as being non-abrasive
on the label.  Some of the other combo-products are noted as being
light-abrasive where the cleaner-onlys seem to be more like a rubbing
compound.

Anyway... the results were pretty good.  I found that it took alot of
elbow-grease, a tall step ladder, and lots of soft rags - they load up
pretty fast.  The key was to use the stuff like a rubbing compound at first,
as it only seemed to lift the oxidization while it was wet.  Then apply
another coat and let dry and polish like a wax.  I did both of these steps
twice and it might have used a third coat, but I was tired and satisfied
after the third.

Don't know if this is the answer for you, just reporting on my experience
with my top.  I suppose you could use a power buffer to go at it if it is
really bad.

Brian