Yeah, I'd phone Seat UK and ask if they know if it's been done / flagged to be done. The couple of times I've spoke to them they've been alright. If they don't know, next cheapest option would be to pay the £30 diagnostics fee. Trouble is, Terraclean will do next to nothing and it's money you could have put towards a new EGR valve. Even if it does work, it's just delaying the
problem. I believe when I had my FR+ and thought the EGR valve had gone it was something like £600 I was quoted to get it fixed. So you may want to prepare for the worst. But I'd have to double check the price. If Seat aren't going to
help, would be worth looking for decent Indy garages in your area as they will likely charge £30+ less per hour.
Edited:
Just checked, it was £600 I was quoted by an indy for a new EGR valve all in, that was for a 2.0TDI (CR) so will vary depending on how much of a pain it is to get to on your engine.