Like was said helps flow out for paint,varnish. If you use it like I said it will act the way armorall does for plastic,tires etc. The difference is this stuff will dry and not wash off. The stuff is cheap and worth trying before spending a bunch of cash refinishing or whatever. Try a small area and see if it works. If you scratch it just wipe more on. Like paint though you want to do it on a windless day to keep stuff sticking to it.

I just used it on a old clear anodized Bimini frame that was clouded. Wiped it with Penetrol and it looks nice and has a shine.

There's only two types that I've seen. I found both at depot. Regular and Marine Penetrol. Recently I tried to find the marine version and it's no where to be found. I think it's all the same stuff.