I opened up one that I have, and it looks like there's a bit of grease in there, but it would take a pretty small needle to get more in.
That is the "standard" unit on MGB's, Triumphs, etc, so maybe Moss Motors can help you.
Never seen a reference to alternate gears for T9, usually you have the speedo regeared to suit the cable revs per mile.
I got a price to redo my Smith's recently, $250-300.
For that money, I'll just use a Racetech unit with electric sender
There are cheap GPS speedos on fleabay