Yes, the BG engineers are happy to condemn the whole boiler just because the 'temp fix' they made is not an original spare. The stupid thing is, they gunged some stuff that looks like silicone sealant where the original was, and it looks much better and stronger than the original seal!
I have a similar problem, my flomatic desperately needs a 4039 Seal which Vokera have no stock of. Please let us know if there is anywhere which may have one of these parts still in stock!