If you're looking for an actual glue pen like a glue stick, these glue stick caps are amazing and made by a small business quilter:
https://krebsbachhuber-crafts.square...cision-tip/111
They're cheaper on her website because the price includes shipping within the US. If you prefer to buy from a larger company, Paper Pieces also carries them though you'll have to pay shipping:
https://paperpieces.com/products/glu...7Bor8k14&gQT=1
They work best with Elmer's glue sticks and the opening is 1/4in but you can obviously just tilt it to control the width of your glue line. I've never had an issue with Elmer's glue washing out.