You do not need to get the deck serviced every year. The service interval should be determined by the number of hours and the type of tape you use. My D7 is coming up on it's 11th summer and the first time it was serviced was last fall. I should have sent it in before but I didn't because I really didn't expect it to last this long. The main thing with these decks is that they have little heads and little motors. The 90m tapes do wear on the motors more than the 60m tapes. The more you use the motors (rewinding and cue) the faster they wear. That said, I ran my deck for 6 years before I started to see any issues and now even after service I still have the issue with the time code skipping during rewind. Other than that it is rock solid and Paul said it had no errors during the tests he ran after the maintenance visit.
You shouldn't be buying TDK DAT tapes at Guitar Center - too expensive. I use the 60m (120minute) DDS HS4 Maxell's from Doug Oade, although other vendors are very good too. The HS4s are the only DATs that have been solid for me over the last 3 years. The Sonys have load issues in my deck since Sony changed the shell design. They used to have the best shell, now I think the Maxell does (of the tapes I use - hhb are awesome in all regards but I don't have that kind of money for media). Different people do report different results. I think it has something to do with the individual deck and tolerances of it's transport adjustments.
Those hours you mention just don't seem right. I think that deck had more hours than that before you got it. As I mentioned, I had 6 years on my deck (probably close to 700 hrs) before I saw any issue that might be motor related and even now it's not a problem rewinding since I've gone exclusively to 60m tapes. If I were you I'd send that deck in for a tune up and also I'd sell those 90m tapes to someone with a strong deck and buy some 60m tapes. I completely blew off all the warnings about 90m tape and I did fine for a long time but as soon as I started to see some issues, I went with the 60s and I think that allowed me to keep running without further damage. In any case, I ran 90m tapes without an issue for many many years. A D8 with 65 hours should be strong enough to tow a small boat. Paul can assess the transport and estimate the true hours. It may actually have less than 100 hours and just need a lube and alignment. Honestly, there wouldn't be so many people fluffing ProDigital if they weren't so good.