I doubt that you will have any luck with the sealer, but if you do use any, be sure to know exactly what you are putting in and label the system very conspicuously to warn future service technicians.

The stuff sold at the big-box parts stores will almost certainly not help at all. Especially be wary of so-called "o-ring conditioners" which can cause leaks where none existed previously.

Cryoseal is one product that might actually work. This is something that you get installed at a shop, rather than attempt to do yourself. They shrink-wrap the service ports to prevent disasters in the future. But still, although it might work, I would bit the big bullet and pull the dash.

That is, if you are 100% sure that you have an evaporator leak. There is a test fitting which bolts on in place of the expansion valve to charge the evaporator with nitrogen.