I recently picked up a Dspiae fountain pen to use with Tamiya style panel liner. This thing is great no blobs or runs from the brush. Does a super fine line. Virtually no clean up. I've used it to apply Tamiya to about 5-6 ABS kits so far with zero cracking or bleeding issues since it uses so much less ink. It was live $5 on AliExpress with three extra nibs. But you can just pick up a fine point calligraphy pen at a hobby or office store.