I think it is rather unlikely that relatively recent DEC
machines had any asbestos in them. Possibly some very old
machines from the 1950's and 1960's might. I know some old
PDP-8's had mercury power contactors in them. I can't
imagine where one would use asbestos in a computer. You
mention tape drive braking mechanisms. I don't recall ANY
DEC tape drive that had a "braking mechanism", all control
of the reels was done electronically.
Jon