Rubber parts started to fail at 54000 miles. Replaced lower coolant hose and all belts. These parts are not expensive if you steer clear of Jag dealers. Parts are available at large chain parts stores, but you have to call around.
Tachometer stopped working at 55000 miles. I thought it was a bad gage and ordered a used one from a mail order used Jag parts house. It cost $70.00. Here's a tip if this happens to you. Bench test the old part before buying another one. Most parts houses won't take back electrical parts. Take the tach out of the dash and, with jumper wires, hook the red wire to a good positive source. The transmission kick-down switch works well. Hook the black wire to a good ground (earth). Hook the yellow wire to the positive side of the ignition coil. Keep the gage insulated from touching the engine. I placed the tach in a small cardboard box on a shop towel. Start the engine. Tach should work if there is nothing wrong with it. Problem seems to be in the ignition box. I switched the feed wire to the tach from the ignition control box (white wire with green stripe) to the positive terminal on the coil. Works great.
Replaced tires at 56000 miles with Yokohama T4's size 215 70 15's. This is a T rated tire, but they look dynamite with an aggressive tread pattern. These tires show no wear at all, so far. While the speed rating is lower than what the manufacture calls for, who really drives faster than 100 MPH for sustained distances? If you do, shame on you!
My XJS has wire wheels with tubes (bladders). My tires would go flat often. I replaced the tubes with new ones when I had the tires mounted. It can be difficult to find a tire shop willing to work on automotive wheels with tubes. I don't know why. I watched the mechanic change the tires and it didn't seem that much more involved than regular tubeless mountings.
I have some rust on the bottom edge of the trunk lid. I found a rust free lid in California for 300 bucks.
At 58000 miles the generator went bad. I replaced it with a rebuilt Lucas unit, but I'm not sure it's charging at full capacity. The voltmeter likes to hang around 9 to 10 volts while idling in traffic. Rebuilt generator cost me $70.00, significantly less than a new one. If I have to replace it again, I'll change it over to a GM one wire unit. One other thing. Why couldn't the engineers put the generator up high and the smog pump down low?
At 55000 miles the power antenna stopped working. Replaced it with a cheaper mail order unit. Worked great for four months. Won't go down the last four inches now.
The wipers occasionally refuse to work and they won't return to the parked position when shut off.
The leather seats are a little scuffed and the stitching on the front seats has failed due to dry rot.
The engine and transmission leak from just about every seal, but not too bad.
I was surprised when I changed the oil and found out that this engine has an 11 quart sump! Where does all that oil go?