AA- 716461 766460 66 50000 November 6 1925
is is for sure a 66 - a drop in bobbin and no extra bobbin case
I recently got a 99 with a 'froze up' foot bar - I really globbed on sewing machine oil and worked it GENTLY until it moved then cleaned the oil off and that cleaned it enough so it works fine now...
you could try that - oil won't hurt anything
dont' force it
you can use car wax on the machine but make absolutely sure that the wax has no abrasives and is safe for 'clear coat' finishes