I have had significant experience with this motor, and this joint.
The end of the tube seats into the housing with a SPECIAL oring seal. They used square cross section o rings.
Go to the Volvo site, they have all the manuals, shop and parts, that can be downloaded.
loosen the bolts, and tap around the housing to free i tup from the bolt faces. Leave the bolts in place, just loosen them. Get the housing free floating with the bolts in place.
Then tap the housing away from the tube, slowly, take it easy. use wooden or brass drifts or blocks. it will break free, but by leaving the bolts in and just loose, you prevent the housing from cocking and bending the end of the tube. if you bend the housing down and away to break it free from the tube, you'll damage the tube and it wont seal again.
Prior to removing, lube the joint over a couple of days with a silicone lubricant, not an aggresive penetrating oil. The seal will swell, making the job worse.
anyone with these motors needs to know that there are tiny water passages in the coolant jackets, and if those plug your engine will be trash. these engines must be flushed with a chemical flush to clean those passages, and should be flushed several times during the process.
The best day of my boating life was the day I tore that md7a down, and tossed it over the side onto the ground. This engine should not be rebuilt. I rebuilt mine, and it was a waste of 3500 bucks. it lasted 2 seasons after rebuild.
"Volvo Green makes me Mean!"