Windscreen fitting companies are reluctant do do the job as they are liable if the glass brakes during removal, and I don't blame them.
Its risky and heated rear screens are quite expensive.
An independent fitter may take the job with the understanding if it shatters they are not responsible, one of the guys working for the big companies may also take the job as a homer under the same understanding if you approach them.
And the good news is if you are unfortunate and it shatters then it was technically accidental and the insurance will cover you.
I can give you some tips to test the seal before you go further but it requires the car to be dry preferably inside and access to an airline