Removing the oil pan isn't "necessary" but it's the correct way to do it according to the factory.
Some have used lube on the seal and it didn't cause leaks so that's not the problem. If the shop went to replace everything a second time I'm sure they checked that it's not the valve cover or turbo oil lines.
It's very straight forward so I don't know what could be going wrong. The only trick is to use the plastic guide to slide it on so that the seal doesn't get folded over. And if you use the plastic guide it's pretty much impossible to damage the lip. Perhaps they are over tightening and cracking the flange? The obvious thing to check is for cracks in the oil pan or flange or that the correct seal is being used.
Some have used lube on the seal and it didn't cause leaks so that's not the problem. If the shop went to replace everything a second time I'm sure they checked that it's not the valve cover or turbo oil lines.
It's very straight forward so I don't know what could be going wrong. The only trick is to use the plastic guide to slide it on so that the seal doesn't get folded over. And if you use the plastic guide it's pretty much impossible to damage the lip. Perhaps they are over tightening and cracking the flange? The obvious thing to check is for cracks in the oil pan or flange or that the correct seal is being used.