Hi guys, I bought a little federal dti today at a car show, it was £4 and I wasn't leaving it there for that price

Thing is, it's a little sticky, in that it doesn't return all the way back to zero smoothly. But rather goes back to a few marks before and then creeps over the course of a few seconds. If you tap the dial gently it will go back faster.
Do you guys think this is just dirty? Is it a diy fix or should I get it professionally serviced?
It's quite sensitive at .002mm

