Draper R850V Router failed speed control (power electronics question)

I have a Draper R850V router. After many years use the speed control failed this morning.

Taking off the top to reveal the "gubbins" I see all the control electronics is potted in resin.

My instinct is to change the Triac (BTB12) as I reckon this must have failed.

Is this a good diagnosis? Could it be something else?

I don't see that a repair I do can be any other than a bit of a bodge.....are there people out there who sell the whole control assembly?

Pic here:

David