I've had 3 years and 50k plus miles of trouble free motoring from my 1999 156 2.0TS Selespeed. She's now done 104k miles and I've hit my first snag. When the car is hot and the gearbox in city mode, it gets stuck in 5th gear. It won't boot down to 4th and if I try to change down manually, I get neutral (although N doesn't display on the dash). When in manual, either from the steering wheel or gear lever, it still won't change down unless I press the button or pull the lever twice, after a 2-3 seconds pause between actions. It will then go into 4th and behave normally. It's like double declutching, it's as if there's one action to change out of 5th to neutral and then another to select 4th. I have no warning lights on the dashboard, the selespeed oil level is good, the pump runs up on first opening the car as normal, in fact everything seems to work fine except this problem.
Now, I can drive around it (in fact I did a 500 mile round trip to the West Country at the weekend with no other problems) but is this the first sign that the gearbox is on its way out? Could this just be the actuator or something else relatively simple that I can check and get repaired? Obviously, the car isn't worth that much so it might not be economically viable to fork out for major repairs.
I'd appreciate any advice out there. Thanks in advance.