Always amazed with how many people will pay $ 10,000 for mower then decide to cheap out on the filters for the sake of $ 10
If the oil is dirty looking then the filter is not doing its job
Hydro filters are usually in the 10 to 30 micron range
Engine oil filters are usually in the 50 to 200 micron range so mr too cheap for his own good could well have stuffed a $ 1500 hydro in order to save $ 10 on a filter
Go to https://www.simplicitymfg.com/na/en_...t/manuals.html
and download the owners, parts & service manual .
The parts manual should also have the model number of the tranny
If not it should be on a sticker , both sides of the tranny and usually on the top as well.
Whatever the recommended oil viscosity is recommended, go up one grade heavier to compensate for Mr Too Cheaps stupidity
Some times you are lucky and it will run fine for many years , if not all it has cost is a couple of quarts of oil .
Hydros are very simple and very easy to repair but you have to be surgically clean
So when I used to do them it was degrease then soda blast then pressure wash then pull apart
When ever the box was open it got covered by a damp shop towel.
Hydro work was done in the workshop shower after the walls & floor were washed down.
Dust is your enemy which should be obvious if you are using a 10 micron filter.