NAPA 1334 is a good match for a 3510i, too. That advice came from the dealer (he's 150 miles + a ferry ride away). He didn't have a suggestion for the hydraulic filters, but the new dealer nearby (35 miles) can get the "official" ones for me. "My" dealer could get them, too.
By the way, On the 3510i hydrostatic transmission, there are are two filters, and they line up vertically. In other words, the lower filter blocks access to the upper one.
Last time I changed hydraulic oil & filters, the upper filter had a seal that wouldn't seat correctly. But ... you don't know there's a problem until you
- install both filters and
- add the fluid and
- run the engine and
- try out the hydraulics.
Well, the upper filter leaked. I drained the system and removed both filters. I checked the seal on the upper one and it looked OK. I simply assumed that I wasn't careful enough when I installed it the
first time.
So I carefully reinstalled both filters, added the fluid, and tested. Still leaking! So I went through the whole process again - drain, remove and replace filters, add oil. But this time I swapped the location of the filters. The problem followed the bad filter - now the bottom filter leaked. At least now the good filter was on top, and the bad one on the bottom. Ordered a new filter. Did the whole thing again.Voilà! The newest filter (now on the bottom) was good.
The cost of that bad filter: $30 for the filter, 2 trips to and from dealer, at least ½ gallon of fluid (most of it spilling on my face and hair), a heck of a lot of cat litter, and at least 10 extra hours wasted laying on my back. On the other hand, I did improve my vocabulary - but it would have been cheaper and faster to take an English class at the local college. My wife's comment: at least the spilled oil didn't stain the driveway like used engine oil does.
For what it's worth, I got used to spending a lot of time scrunched tight underneath a leaky engine (read: hot oil in my face). Back in my hippy-ish days I had 3 VWs - at the same time! For those who don't know or don't want to remember, the old VW pancake engines needed almost constant adjusting on the cylinder #3 exhaust value - adjusted hot, of course. If you didn't keep it adjusted, you'd blow the engine. When I got rid of the last VW, I had to figure out what to do with all that free time!
Dr. Murphy is always lurking near me, and his Laws are nasty! The good news: Mighty Mo (my wife's name for the Branson) has lots of room for servicing.