Probably needs to be recondtioned. Relatively easy, but not necessarily inexpensive.
Usually, this consists of cleaning all switches and controls, replacing capacitors, adjusting bias, DC offset, etc.
Whether or not it's worth it depends on how attached you are to the gear.
AudioKarma.org has a large vintage following that would be happy to provide plenty of advice and recommendations on the problem.
Just because there is a knob doesn't mean you should turn it.