Paul, if it were our OC I would hope that we would NOT agree to sign, as it could be the Owner is just trying to ‘tidy things up’ before selling.
If you all agree to the demands, it is possible he gets a higher price for his property after not paying his correct proportion of levies for 20 years.
I would be asking for him to pay back the outstanding additional levies plus interest, so the current OC benefits, before agreeing to anything.
I do not know if that is legal, but is certainly sounds fishy he is in such a rush to get things sorted out now.