Homebrew PCBs

Hello All,
I have a fairly complicated single-sided pcb that I am doing with
toner transfer. The tracks and through-hole component pads are 12 mil.
After several tries at T/T I have reached a 99.99% level of transfer.
I wish to touch up the missing bits. However, the examples of a
sharpie that I have seen here in OZ would be like trying to touch-up
with a broomstick (and they call them fine point!!). So I am looking
for advice and experience in touching up fine track resist; including
make and model of   known successful products.
TIA
Regards
John C