I have the big Oster body clippers; they're about 15 years old and have clipped about 12 horses total. I put them away for about 10 years and got them out last fall. Again this spring. So not used a lot but "old".
Something isn't right. The housing gets too hot to hold and the bottom of the clipper blade (the horse side) gets pretty darn hot. This heat comes after about 10 minutes of use. Then they won't clip well either. I did his shoulder and chest the other day and it turned out great. Daughter had done her horse a few days prior with a different set of blades. Today, I tried to do more clipping and got just one side of his ribs done nice. The other side is a hack job.
Do I need new clippers? Is it worth it to have these reconditioned? All the blades were sharpened this spring by a sharpening business used by most of the Morgan owners in the area...so not a Mickey Mouse outfit.
Have you taken the blades off, pulled off the "square" on the drive shaft, cleaned everything out really really well, and oiled at the appropriate parts? If that does not work, then google oster and find a dealer that will check them out. Those clippers are too expensive to give up on. I have used mine for the past 16 years, many times a year, and they are still working well.