Some times you can get a bit more life out of them by draining the oil and refilling with something a bit thicker.
IF they are worn out, they should work fine first off then get weaker as they heat up ( usually noisier as well )
If they just stopped working without warning then suspect a broken belt, broken pulley or stuck bypass valve.
Hydro gear do sell rebuild kits which will work out about 1/2 to 2/3 the price of replacement.
Just remember they are made is dust free sterile enviroment and you need to do the same.
I use the bathroom in the workshop, spray the walls down and keep the trannies covered with a damp rag.
This is after washing degreasing washing again, soda blasting & rinsing off the outside
