Better still use a white based 2w bulb sold for the VW T25 clocks.
Don't bother with led versions - the ones I've tried have been a poor fit and contacts go iffy after a few days.
As the access to the back of the clocks, including the vacuum pipe is such a swine to achieve, the last thing you want is to have to pull the clocks out a few days later when the aftermarket LEDs start playing up!