A freind bought an old double bass had major grooves in the fingerboard, now i no it wanted plaining down but he was skint , so we tried different fillers and they were ok for a while but kept falling out . This is were i had a go i was going to use epoxy glue when mixed together sticks like sh*t and its hard as hell , when i came across this stuff called MILLIPUT EPOXY PUTTY its like plastercine to the touch or bluetack two different colors mix them together as a test peice never seen anything as hard ,you can sand it drill it tap it out and its awsome . I sanded the board cleaned it, filled the grooves, 8 hours to set properly, started sanding and shaping ,got the fingerboard back to shape no grooves and you cant see it because it dries black, 10 gigs later not a mark in the milliput and no buzzing of the strings like there was with the grooves .
now anyone who repairs double basses and dresses the board knows this is the correct way to do it, but when my mate got a quote of a luithier for nearly £200 he fell through the floor, times are hard so if you want to try this stuff its a fantastic filler hard as hell even sets under water sandable and you can paint it you can even smooth it with water as your filling so minimal sanding afterwards.So before you say get it done properly when your skint your skint and needs must and it dosnt alter the tone in anyway and it really works
picture below hope this helps somebody sometime