Join Date: May 2005
Location: Mayenne France
My Motorhome: Carthago
Thanked 242 Times in 219 Posts
Dependant on which sealant has been used it is very possible for what appears to be a good seal but still be one that allows water through.
The plastic that Heki vents are made from will resist attachment from most silicone and the normally used Sikaflex products.
My suggestion would be to remove the vent completely and thoroughly clean the mating surfaces, then using either a ribbon strip or a butyl mastic, for a secure and lasting seal.