We recently had the same John Deere exhaust repair to do on two separate tractors. The problem was joint flange failure while the rest of the exhaust was still quite good and since new John Deere parts are going on £900 we thought we might be able to save the customer a little money here. We came up with a solution by making new flanges to weld to the existing exhaust, see pictures. So if anyone would like this or a similar job done, to a JD or any other make, please get in touch or we could just sell you the flanges. Making these is quite a fiddly job so, to sell you the parts, we would require £65 each plus VAT, a lot less than new JD parts. we could knock off £6 each if you required 3 or more. If there is a demand for this servis we would find a cheaper way to make these parts.
I recently found what looks like the female flange on ebay for I believe £29 however it looks thinner than ours.