Rear main seal leak
Is Blue Devil recommended to be used for rear
Blue Devil is a band aid at best. It might work and for some time, but the seal will start leaking again at some point. If you plan on keeping the vehicle long term, repair it properly by having the gasket replaced or just keep adding oil.
You can try but you can't fix a rear main seal with a bottle of gunk.
Stuff like that is only good for seals that have turned hard from lack of use, most rear mains when they start leaking just have to be replaced, and if the crankshaft is grooved a speedy sleeve installed.