Mushroom Vent

[UFO]

I have removed and resealed the rooflights on our 2009 Adria Twin as they were leaking. Other than these the only other 'holes' in the roof are the solar panel cable box, which is Sikaflexed so should not leak, and the bathroom vent. I want to take the vent off and reseal it. Before I tackle it I thought I would ask if anyone knows how they go together / come apart. There are four lugs on the dome that can be pushed in, see photo. After 12 years in the sun these plastic parts may have become brittle. On YouTube I saw a similar vent, on a caravan, being repaired where the inside fitting was pulled / twisted off revealing fixing screws underneath.

A diagram would be nice but guidance from anyone who has personal knowledge of these mushroom vents would be appreciated.

 

[Caz]

I had one like that on my Win. It was right above my bed and I used to stuff a sock in it to stop the draught. I had it taken off and capped as it was in the way of where the solar panel went.
I have no idea how it comes off but suspect the lads that did it just used the "brute force and ignorance" method as they weren't putting it back on. I can ask them, if you like.