I have an old Permagreen Ultra. Last week it started making a chirping squeak sound at times. Only when moving. I cannot locate the source of the sound, but possibly it is from the front wheels or near there. So...I found the rubber oil filler plug on top of the tranny--and added about 1/3 bottle of gear oil. Anybody know how much to add or how to check this? Source of squeaks? It is running OK--but--5 dollars for gear oil is a lot easier than a new tranny.