Over the last 18 months / 17000 miles of ownership I've had to replace:
Exhaust system
Rear wheel bearings (centre bearing went)
Regulator/rectifier
Fork seals
Rear shocks
Ignition lock (keys kept falling out when switched on)
Front brake callipers (previous owner had fitted Suzuki slabside GSXR ones, which were pretty poor)
Seat cover.
I bought this for £700 as an MOT failure, requiring replacement fork seals and rear shocks. Investing in a pair of hagons and some seals, all of which I fitted myself, I quickly had a road legal, big shaft-driven touring bike.
The previous owner had fitted K&N filters and rejetted the carbs, which meant the bike ran terribly and returned about 30mpg. I replaced the carbs and filters with original Yamaha items (after a real job refitting the original air box), after which it ran perfectly.
3 months after I bought it, I fitted hard luggage to it and I set off on a 4500 mile tour to the North Cape of Norway, mainland Europe's most northerly point. The bike ran perfecly and in touring mode on the narrow roads of Scandinavia, returned 65mpg cruising at 60-70mph. This can drop to low 40s on long, high speed motorway blasts.
The bike was perfectly comfortable and I did 3 500+ mile days in a row without feeling any pain.
Since then it's been on several tours around Scotland (where I live) and one 2500 mile trip to the Swiss Alps with a pillion, as well as year round commuting through the worst of Scottish weather.
There have been a few problems (regulator / rectifier going which stopped it from charging for example) but parts are readily available cheaply from ebay. I recently picked up a complete spare engine for £30 for example!
The bike isn't the best handling or fastest of bikes, but it's got great mid range torque and can hold its own in most conditions. It's also easy to maintain, and after the hassles of chain driven bikes, the shaft drive is excellent!
I've considered upgrading to a diversion 900, the XJ900F's replacement, but apart from more modern looks, I don't think I'd gain anything.
I too have an XJ900, but a 1983 model. They are excellent all rounders and very easy to live with, especially in the hot Australian conditions.
Thanks.