2001 V70 XC 5 speed auto, 2.3 litre 247HP high pressure turbo.

When cold, the changes are near perfect. Once hot, the box flares between 2-3, and 3-4. It also can be slow to change down from 4-3, and 3-2, but not every time. It can also produce a definite thump on the change down between 3-2 at low speeds (as in slowing to turn a street corner).

When operated in tiptronic mode, it usually changes reasonably well, although sometimes it seems to be a little slow in reacting. The other thing I have noticed is that when at steady speed, the engine revs seem to be fluctuating very slightly. Not enough to actually read the variation on the rev counter, but you can see the needle wavering, and you can just hear it.

I’ve just changed the B4 servo cover (and the o-ring on the piston), and the gearbox has had a full flush with Mobil 3309 ATF. No faults are showing on scan. The service message was reset following the flush. The fluid was very black, but did not smell burnt, nor were there any obvious particles of anything. The car has done 247,000kms. Converter stall speed seems about right.

I suspect something like a sticking piston in the valve body: anyone got any ideas as to what it could be, please?