1964Hr 753 bobcat. when it warms up loses power on the left side in reverse. been that way for several years, doesnt get used alot. seems to be getting worse. also now i noticed it seems to have a hydraulic whine where it didnt before. [maybe that is because i put a new belt and muffler on recently]. i service the filters regularly and looked at the lh case drain filter. case drain filters were replaced at about 1200hrs. inside the filter showed no metal, clean oil color but what appeares to be mummified bug parts but not alot. i dont believe it has been whining before or at least not as bad. no problems at all with the hydraulic cylinders. how do i ck for a bad motor or pump asm?