Congrats you were able to get the pump union loose. I too have the same problem. I have to replace a dripping Gate Valve and have tried everything. Two different wrenches as shown here. It's the weird angle and no room to grip the wrench. Also no room for the screwdriver / hammer method. I can reach all the other unions in the tub except this one, but the exit pump union, can not get a grip on the pump union. I was thinking of trying cutting, drumell tool, hack saw, but don't want to damage threads on the pump, since I will need to tighten the new ring.....but can't get angle to tighten.....
Did you replace the O-ring and fix the leak?