Tractors about 25 years old. I use 134 hydraulic or transmission fluid which operates forward, reverse and all lift mechanisms. I have two filters for this system, one called a line filter and the other a suction filter. Each, from Ford, costs around $33. I wonder if there are cheaper (in cost) filters available or if you can use a car engine filter if the threads fit? One gets replace every 100 hours, the other 200 hours. thanks