It is a well known fact with these old Motorhomes and Campervans and more so the Talbot Express also the Citroen C25, MK1 Fiat Ducato and Peugeot J5 that when they have been stood for weeks, rain and even snow melt goes through the vents into the air intake box, it then empties through a hole into a drain pipe and in old design fashion it stop right over the top of the Talbot Express gearbox, there is a inspection cover on top of the gearbox and the gromit/seal over the years has either deteriorated or disapeared, water then gets into the gearbox and when stood the clutch sticks and you end up unable to select gears.
These magnetic covers for the vent on the Talbot Express cover the vent and stops ingress of rain water and snow melt, these are NOT for driving with these in place.
Then we have the Bonnet Scoop for The Talbot Express, these cover the vents but can be left in place as air can still get in through the vents.