Atwood Hydro Flame 8520, replace or fix?

I looked inside the furnace and saw a little bit of rusty material that has flaked off but not much. Most of it looked pretty good. The exhaust pipe came out with no problem although is has one side party folded in covering about 1/4 of the pipe. I am guessing this is set up like this from the factory. I have cleaned all the contacts so far. I did find this burner assembly at a local supply house for $21 so I ask my wife to pick it up. I am thinking if I replace it and if it works fine I will start looking at a new furnace in the future. If it doesn't help I don't think I will continue with replacing parts on the unit. Now to figure out how hard it will be to get a replacement that fits without a lot of modifications.