I have a pair of Lennox G513 HVAC units cooling the main and second floors
of a residence. The compressor/condenser cabinets are mounted on a concrete
pad positioned away from the main building. The evaporators are integrated
within the 60's era custom, heavy gauge, commercial quality ductwork for the
three furnaces in the residence.

The main floor's compressor is in need of repair/replacement.

I have been told that these units are obsolete, their refrigerant has been
banned and parts are NLA - the recommendation is to replace them with
modern units.

Are these units in fact no longer serviceable?