You're right, there have been prior threads on this, but reiterating their content is easier than finding them.

There is no prohibition against giving a customer a copy of a CTR. If the request is contemporaneous with the transaction there is not a lot to discuss. If the request comes later, the mercenaries among our group would charge a research fee.
Before you procede please note to the customer that copies of the CTRs will not
satisfy the IRS, particularly as to the source of the income they may represent.
The IRS already has copies of the CTRs and its somewhat likely they are the reason they are asking your customer about where some of the money came from.