My main concern is "has started knocking under medium load."
As for the fuel economy, I would think noting that Its started using 9L more per 500km may be useful information to working out whats gone wrong dont you?
FMIC, PFC, Eboost (usually leave it at 1/2 bar when commuting), Turbo back exhaust, Pod and thats about it. No changes here for a couple of years.
Ok, so it wont drift, but any way it could have been reset if the battery was disconnected or something like that?