I've never flown in a Piston Provost, but certainly a poorly-flown stall turn in a Chipmunk could result in fuel escaping from the anti-siphon vents splattering against the cockpit canopy....
The worst honk-inducing smell though, was the horrible rubber smell of the H-type mask...
Although the previous night's 'relaxation' in the OM bar might have been a contributory factor.