gloss is oil based, so any water based produced should be in 90% cases be ok, butt as you say timber movement will as in "timber to brick "there is all ways be an element of movement hairline cracking to pair, the best preparation in my opinion is to if the timber cannot be removed then a good key is needed to be applied , i find as a good proven key is the good old pva,sand,cement slurry is hard to beat, eml the joint between brick and the glossed timber if that is not visible then triple scrim the joint, you've prepared it to the best you can, butt do advise the client that hair line cracks will probably appear.