Tach is slow to respond

Is there anything that I can do to maybe lubricate the inside of the tach or clean it out?
I have it off and it doesn't appear to come apart unless I was to cut the metal band around the housing. Even then, don't really want to do that...Anybody?

pry the bottom of the ring outwards, after prying it all the way around the lower side of it the Tach will open. then all you need is to do your cleaning and lube and carefully mash the ring back into shape best you can.

Car body tools come in handy at this point to make the metal as straight as possible, this is your only option besides sending it to a rebuilder.

Or you can see if somebody is parting out a bike they would be willing to give you the tach off of.