Vinyl has been making a comeback so maybe the DAT will too. MAYBE.I can't imagine it's worth fixing.
Back in my car audio days, if a channel died, or accidentally got 12V shot to it so a customer could save money... It went straight into the trash can.
Even after all these years, I can't imagine a plain cassette deck is worth fixing. (still might be worth saving just in case it's worth something 30 years from now)