Depending on how bad the outer casing is beat up, plastic jb weld will work just fine and give you a strong fix. I have a 1986 Yamaha moto 4 200 and when I bought it, it had cracks, it was beat, missing the element, the filter and the back cap. I repaired the cracks with jb weld, and I bought a 2 1/2 inch pipe to 2 inch pipe conversion for 4 dollars to replace the element, with this I chopped it down to shorten it tp about two inches long, and jb welded that on over the hole to the carb. With that I bought a 20 dollar filter from ebay. It was a 50 mm or 2 inch flange uni airfilter which fits nicely over the end of the conversion pipe. For the back I used some spare plastic laying around, cut it shape, used silicone as a seal and used some screws I had.
Hope this helps
