Humm a rant hey my question is why are you grain filling it anyway, you don't need to grain fill basswood, as for what I use I actually use timber mate to fill dents and deep scratches I use the white one colour it to the stain or dye, I don't use it under lacquer the thinners in the paint makes the timber mate expand then it shrinks back and it keeps doing it for a couple of months, I use lots of different things pending what finish I'm after, so I see you're an expert I remember that so get on with it