The Golf Mk6 Match is a pretty nice car so I don't think you need to go through the stress of PXing it at a Seat dealer. You could try selling it privately otherwise go round the local VW dealers and see how much they'd offer you cash given they can sell it themselves.
That then puts you in a stronger position for buying the new Leon as you can order through a broker at the lowest price. Just try them all and see which is quoting the lowest price
That then puts you in a stronger position for buying the new Leon as you can order through a broker at the lowest price. Just try them all and see which is quoting the lowest price