Your mechanic might be correct about the internal piston SEALS. Why he didn't replace them while you had the OD in to him is beyond me. Even at Volvo's inflated prices of over 5 bucks for each seal it would have been a bargain. Unless he wants to sell you another OD at 1400 bucks? You should be glad he didn't sell you the "cone clutch" since those rarely are the cause of the symptoms you describe.

If the springs in the pressure control valve are OK like John's were not, and the mechanic has replaced the solenoid, then your problem is most likely the actuating piston seals.

Some solenoids have a problem in that over time the fluid can get past internal seals and cause OD self engagement or hold engagement after the OD is "turned off".

From my experience, you are haveing the first throws of actuating piston seal blowby. the unit works fine when cold getting progressively worse as it and the temp warms up until no OD function at all.

Since you have had the OD off, save some $$ by doing the job yourslef. See the 700/900 FAQ's under transmissions for a step by step or request the file from me.

Duane