when i put my thermostat in, first scrapped off all the old sealant. made sure surfaces r clean then apply a lil sealant to the ridge before inserting the thermo (check the lil valve is positioned at top) so that it'll stay in place. then put bead of sealant along the covers mating surface and reinstall.
make sure the thermostat has this lil one-way valve on it (right pic) cos one i got from partco didn't (left pic), which meant the system couldn't fill up. waste of a fiver.
i ended up buyin the proper one from dealership for a tenner.
