Your leaking and running low on fluid lets the direct clutch drum piston lose pressure to hold the clutch's closed tightly making them slip and wear . Most shops never check to see if the Valve body is worn from the input shaft cast iron ring wearing on the valve body letting oil pass into the PG case which is not a sealed unit and causing it to over fill resulting in leaking , even when not driving. Sounds like your problem your having . The only way to correct it is to replace the valve body or find a good one that's not worn as seen in this pic that I've talked about many times to members here. You cant depend on a shop to inspect this area unless you make them aware of this or YOU look to see if it's worn . 99% of shops today don't know to check this out when they have it apart. (YOU NEED TO!) Or copy this pic and show the shop what I'm telling you. I hear about this dam thing all the time and FEW people will listen or read what I'm telling them. NO Mickey Mouse trick will stop your leak or burping if this is the problem period !!!!!!!!! So good luck!