Cees, you are likely correct. The 85-90 is very sticky. I got the car out recently; due to disuse, we replaced the front brake calipers, which were sticking, and also did the rear axle outboard seals, which had been incorrectly installed by a prior owner, years ago- they were leaking.
There are two issues with the car, now- persistent thumping on bumps, which I think might be the Timevalve exhaust system, which doesn't fit very well (this has been a problem since it was installed, it never fit correctly) And the transmission is still hard to shift- it doesn't clash or grind, and it isn't noisy, but it doesn't feel like the BMW Getrag gearbox in BMWs I've owned- the shifting in them was light and precise and easy, even in older cars. I have a good friend who's a transmission specialist (he rebuilt the unit in my E-type and did very well on that one) and I've asked him to drive it and see what he thinks. I can't tell if the difficult shifting is in the linkage, outside the gearbox, or inside it. But all the gears are somewhat hard to engage. Any suggestions?