I just purchased a used 1986 Honda Fourtax 350. I am enjoying cleaning it up. I am going through it and could use some advice on a few things.

The fan that is behind the oil radiator does not seem to work. I do not know if it is broken or only comes on when the temperature reaches a certain degree. Should I replace it or just try and trouble shoot it?

I changed the oil but have not changed the oil filter. Is this like a car and the filter should be changed at the same time? I was thinking about using some slick 50 in the engine to reduce the friction?

The body has been beat to death. The fenders are bolted together with strips of metal. I do not think OEM fenders are available or affordable, I know I can not be the only guy with cracked fenders, are there after market parts or repair ideas out there?

I am sure the air filter could use a cleaning. It looks like a oil bath type. What should I use to clean it? Gas? Then would regular motor oil be the right thing to wet it with?

I would appreciate any Ideas/ Advice on these things or other suggested maintenance .

Thanks.