Hoover frost free fridge/freezer – ice build up in fridge

There was a recent entry on a similar problem but the fridge was working fine. My isn’t! Hence my message ……

Hoover Frost free fridge freezer HF27C 001 – 6 yrs old

Problem:
The ice is building up on the top part of the fridge.
The motor is always on.
The fridge is very very cold. Freezing the veg in the bottom drawer.

I have manually defrosted the unit but overnight the ice re-built.
The drain is clear.
I have cleared the back of the unit.
I have check the door seal.
The seal is broken and I would assume this is the reason why the performance is bad.

Question:
Before I venture to buy and replace the seal (25 quid + my basic knowledge) I would like to know if there could be another reason to the motor + ice problem.

Also I have search and found some advise on how to replace the seal but do you think I really need to take the door down before fitting the seal!?

Thank you 🙂
Didi