Unqualified Opinion
I'm totally unqualified to make a technical judgement on this aircraft, either face to face with it or in the photographs but my gut feeling is that it is one needing very careful consideration.
There is quite a bit of corrosion in the skins, shown by the paint bubbling. The risk with rubbing it down and re-painting is that the corrosion may have gone deep enough to make the remaining good metal too thin to support the loads imposed on it. That skin wrinkle has the appearance of being caused by a blow, a birdstrike perhaps. I don't see rivet lines to internal structure so none there to damage. Washed out ailerons? I haven't been anywhere near a Cessna so can't comment at all on that one. Rusty connection rods are easily replaced and the attitude indicator fault shouldn't be difficult to fix either. Grease can be washed off and new stuff applied. Oil leak - see if you can find out where it is coming from and if it is an engine accessory, that is another easy fix or get professional advice. The trouble is, that aeroplane looks like it hasn't seen proper maintenance for a considerable time, as IO540 says, when you begin to dismantle things to mend them you may find more things to fix. Generally, the deeper you go, the more expensive it is. You have given no indication of mechanical wear which could be another major expense.
If you started your driving career with a really old car you'll know that for a short while it will be your pride and joy but always having to fix it before going anywhere soon makes it into a disappointment and money sink. There have been many thousands of C150s built, save your cash and wait till a good one turns up or invest in a thorough, independant survey and come to a compromise price with the current owner. Is there any prospect of buying in the States and having someone fly it down for you, or are the rules too inflexible? Regards, Aerials