[MWMan]

Thanks for this - very interesting. After fitting the blower motor and proving it OK, I put all the carpets and trim back in. Almost immediately I ran into another problem, which looks like the fuel pump and sender unit. I have ordered these and will be changing them at the weekend, once the parts arrive.
Based on your findings, I think I will remove the carpets again and check for water. If there is some in there (we have had a lot of rain since I changed the blower), I will do the same as you with regards to sealant, and see if that works.
Many thanks for this and for looking at the sunroof, which is still a mystery!