looking to buy an early '80s Boss DM-3
what about the components inside

as long as they werent kept in a damp cellar they should be good.

i got a bunch of old pedals in my closit. . loaned them to my brother and his wife put them in the cellar. they were covered with this green corosion. cleaned them up and everything worked fine on all of them. and there from late 70s.

As long as it's in good shape go for it. I wish I never sold mine. Just keep in mind that the DM-2 and DM-3 use the old style Boss adapter.