Thats a really nice bike and quality build I would say 2k- 2500 in that condition cleaned up could be worth more. The 50 mods don't fetch as much as the 110 mods do but thats still a nice bike.
With it being that dirty on the inside I would check the crank seal. When dirt and water gets into the cover it can make the seal fail.
The 06/07 are the exact same bike with a different vin number and decals. The 05 has a different shock, brakes, crank, etc. Yours is 06/07
Very nice build. I'm also wondering about how you like the magura on the 250
Replied. For everyone wondering If you call race tech they will give you the shim stack settings for your specific application. You will need shims obviously but to my knowledge the rest of the kit is there.
bump $100
The airbox seal could have failed or the airfilter lip was not sealing properly. A lot of people use rim grease on the filter lip. The air filter cage could also be flexing not creating a good seal. Filter could be leaking around the center screw. Twinair ... more ยป
You install it dry and then leak down test it. If it leaks then you use sealant.
Good deal very nice bike GLWS