Buy your hydraulic filters at any good auto parts store. I've seen the numbers posted here but can get them if you want.
Napa Gold has been mentioned. This is made by and identical to a standard Wix hydraulic filter. When I noticed that (at the Napa store, I use Wix but thought "Napa Gold" must be even better) the Napa guy said that the regular Napa filters were a cheaper line than the regular Wix. Wix has always had a lower cost line (ProTec) and that's what Napa was buying. The Napa Gold cost a little more than the comparable Wix. Either is just fine.
Background (for someone so totally bored to have read this far without dozing off): when I first started working at an auto parts store (16 years ago, lasted for 6 years) I had questions nobody could answer on filter construction.
The store let me buy as many filters as I could find and, in additon to the ones we carried, cut them all open. What a learning experience that was!! I had been refusing to use ProTec filters and instead spent more to get Fram. But that is where Fram's money goes: marketing to get people to buy their filters, not into the quality of the filter.
Now I'll use Napa, Wix, Amsoil (the new EA filters especially), and CarQuest (made by Wix). I won't use Fram. The worst at that time was one made by Purolator and marketed under the Bowles brand --- sold by trucks to the shops, and built so to allow "screened" oil (think VW beetle) unless the screen clogged, then it bypassed and washed the clog into the engine with more unfiltered oil. It was the only filter that bragged "full-flow" on the box and the ony one that didn't force the full flow of oil through the filter element.
I'll stop now before I nod off.
I just got my first parts order from PT today: new brush hog blades and bolts and spacers. $97, so it was easy to meet the $50 minimum order.
Phil