[mds]

The B4 Solenoid is a fiddle to do but not difficult Volvo sell the repair kit (they call it a piston repair kit Rufe on here can help Doves if your desperate) its not expensive about £15 I think.
I used to have several V70 P2 in my business we had the flaring between 2/3rd changes on 3 of them as a precaution we changed the B4 cover on all 6 I also got into the habit of flushing the ATF every 50k after reading up on the American Forums (year was 2002).
You will need room to work under the car so up on stands or ramps. Take off the under tray M10 bolts if I remember.
At the rear of the transmission angled down you will see a large (about 60mm dia) cap with a raised cross on it, this is held in by an internal circlip. Remove the circlip access is tight but you can reach. With a large pair of grips rotate the cap using the raised cross the spring pressure will push it out, have some rag ready there will be a dribble of oil if the piston comes out push it back in.
Inside the cap you will see a hardened washer if this is loose or has come away that is your problem.
Use transmission fluid to lubricate the "O" rings on the new cap and push it in fit the new circlip, clean the area run the engine and check for leaks. Replace the under tray job done. Myself and one of my engineers became pretty quick after the first couple.
Finally Flush the Transmission then go to Doves to have the fluid counter reset and software upgraded. My understanding is you should only need Adaption if you have had major surgery on the gearbox.

When I sold the business I kept 2 of the cars and one of the engineers took one to be his personal car he is now over 250k and pulls a caravan?
So with good maintenance these boxes are tough.

Have you had the codes checked to make sure you don't have other issues?? You are not far away and I have a reader if you don't?