Hello, my name is Mark and I will try help you with this.
The list of faults certainly can be expensive to repair if the worst case scenario was to happen.
ie. You needed to remove the cylinder head to then remove stuck injectors.
It is unlikely that a sealant in the cooling system has blocked the pipes or heater matrix. That's not how sealing compounds work.
If the aircon is needing recharged then before that is done it needs to be pressure tested for leaks.
If leaks are found then depending on where or what will affect the cost of repair.
If there is no leaks and the loss is due to natural escape over time then refilling the aircon is about £50 -£80 on average.
I cant advise on local garages as I don't live in your area but you can check online at sites like the good garage guide for information.
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