Let's back up the train.
The investor YOU dealt with is saying a cure must be done.
They are looking to YOU to get it done because their contract is with YOU, not the broker you have a contract with.
If you can recoup it from the broker, fine.
If not, in order to get the loan purchased, you're going to have to pay the cure.
The part of your original post that I see as a problem is:
Broker issued an initial GFE. As a lender, we issued our GFE to match exactly what the broker disclosed exactly. Any redisclosed GFEs were at the request of the broker and list fees exactly as requested by broker.
imho, you shouldn't be laying the blame on the broker. Who's in charge, the broker or the lender? RESPA says it's the lender. Therefore, you need to be sure that what you're doing is correct by the Reg, not by what the broker requests.