Good day Tomcat,
I'm new to this and French Canadian so I might be short on words or expressions sometimes but, don't worry, I've got exactly the same tractor as you have and parts are easily availaible. Problem is that some dealer won't recognise grey market and say that they don't have the parts so, you'll have to play a little game.
Your tractor is a mix of B6000 and B7100 so, once you've identified the part, look it up in one of the book and tell the dealer it's for a B6000 or B7100 with the part number from the part book. They're available for free on the net. But, if you want to be sure that you've got the right part, send an EMail to Vic at ancreage outfitters and he'll provide you with a paper copy of the original Japanese manual.
acreageoutfitters@hotmail.com
then you cross refenrence your numbers and you'll be sure to get the right part. Regarding your Transmission/differential/hydrolique filter, the part number is 66021-36390 and the recommanded oil is TDH, not 90. If you have any other questions don't hesitate but don't expect an answer to soon as I open up my computer once every other day. Good luck.