At this point it doesn't really matter. First off, running in anamorphic mode will give you more resolution, and neither method will wear the tubes more, since tube wear depends on the amount of phosphor you're using and how hard you're running the contrast. So either way you're using a 16:9 area, so the tubes will wear equally fast whatever way you project the 16:9 image.
Second, no offense, but the Selecos were poorly made compared to other sets, and very few were sold in Canada. I have had three through here in the approx 5000 sets I've had in, and I parted all of them out, as I couldn't trust the build quality to last. Two of the three had blown up power supplies with smoked boards and parts, so all I got out of them were the tubes, and threw the rest out.
So considering that you (or the previous owner) got 4000 hours out of it so far, I'd say you're on borrowed time.
So run it as lightly or as hard as you want.
Assuming that they are the focus pots and not the G2/master brightness controls, sure, unstick the pots and tweak them, as at 4000 hours they most likely will need a bit of tweaking. Tweak one pot very slowly. If the focus doesn't change, put it back exactly where it was, and reseal it.
The blue tube does wear first. Not sure why, it's been debated here in the past with no one really solid answer as to why.
Run it for as long as it stays alive. Who knows, maybe you have one that will outlast the others, but don't spend any money on it if it dies.. There's higher end sets out there for dirt cheap or free..