for my 07 XT225 are there any parts I should buy before they are obsolete or hard to find?
air filter, oil filter, brakes….the stuff most likely to need?

Both the air and oil filters can be cleaned and reused. I'm not sure how common the brakes are.

What is your mix of road and off road riding? Also how hard do you ride? This matters on what parts fail and how soon. We kept a lot of spare parts in stock which might be overkill if you're riding mostly street. The pleated barrel filter needs to be inspected for cracks in the pleat folds and the rubber gasket on the end. That said, you can get many oil change cycles out of that filter. I cleaned it with a soft tooth brush and diesel fuel. As for the basket filter behind the oil drain plug, inspect the plastic ring on the base. Then there are the O-rings.

My riding os 50/50 and at this stage I would rate it as easy-moderate riding. Almost no highway, mostly country roads up to 45 mph. My dirt riding is very conservative, getting to old to break my body!
Thanks for any ideas!

This is a great thread. I suggest we all post the year, mileage of our bikes along with any parts that have broken so far. Maybe we will see some common patterns.

I’ll start
2006, 5K miles

Chain slider
Starter relay
Carb joint boot
Carb float
Various carb o rings
Rear break linkage spring (got rusty)

2006
28,000 miles and counting

Carb boot
Starter o-rings
Valve cover o-rings
Seat cover
Handlebars because I crashed and bent them.
All the usual wear items.... tires, brakes, chain & sprockets, light bulbs, etc.

Jeannie and I retired our 2003 XT225s at 15k miles. Almost all trail riding with plenty of crashes which never helped the bikes. That said, those bikes never left us stranded. Parts we kept in stock:

Brake/clutch levers.
Disc pads.
Speedo, clutch and throttle cables.
Headlight bulb.
CDI unit.
Front fork boots.
Fork seals and bushings.
Oil filters.
Drain plug & oil filter cover O-rings.
Oil & grease (Mobil I synthetic)
Main fuse (20A blade)
Bash plate grommet sets.
Spoke set (before we upgraded rear wheels)
Wheel bearings (sealed).
Air filters.
Rubber handlebar grips.
Throttle grip plastic sleeve.
Spark plug and wire.
Horn.
Ignition coil.
Side cover rubber grommets.

I used to keep valve cover O-rings in stock until I replaced them with silicone ones. That's about all I can remember. I may have kept a small collection of nuts, screws and bolts. I know the heads on the side cover screws got buggered but these can be gotten from a HW store. I replaced the starter O-ring with a silicone one but never stocked the OEM part. That's all I can remember some years back now.

2007
1,204 miles

The only part I have replaced is the ignition switch. Lost keys, purely my fault. It won't happen again.
I expect my XT to look and work like new 10 years from now, with no parts other than filters and spark plug. Oh, I guess tires and battery need to be added to that list.

My XT225 is built out of two different bikes, with a lot of aftermarket parts. I have a huge box of both new and used parts, and a nearly complete parts bike with a 3,000 mile engine. Unfortunately I am reaching the point where I may not be able to ride the XT much longer. I have to stand on something to get on and off, and I am hesitant to ride it very far off road. If something were to happen, it might be difficult to get help, and in my condition I could not walk out.

Right now it seems to be mostly plastics that are no longer available. I sold two stock steel fuel tanks and replaced them with 4 gallon Clarke tanks. Earlier this year, I replaced the swing arm bushings and seals, and all the parts in the rear suspension linkage. Everything was available. Chinese carburetors, pistons, and rings are available, but many people have had issues with them. Many mechanical parts from the TTR225 will fit.

2007 XT225 4485 miles

Worked on my list today
On hand:
valve cover gaskets
spark plug
oil filter
oil filter cover oring
oil drain plug oring
oil strainer
air filter
air filter oil (notoil)
air filter cleaner (oxiclean)
fuse
air filter case gasket
grease/lube
Buy when needed:
tires
oil
battery
brakes
What I replaced since 2007 not onhand:
tires
battery
fuel knob
oil
So far this bike has not failed me on many 90+ mile rides in mountains 8000’ - 13000’