Lift dust cover.
Clean around the seal with a piece of suitable plastic. (credit cards too thick / milk carton maybe too thin. Maybe an oil container? ).
If not too thick* you can carefully get it under the edge between fork leg and seal and clean out any muck that's causing the leak ... sometimes - if the leaks not too bad)
With a sharp blade, cut up a tampon to fit above seal / below dust cover.
Slide dust cover back down firmly to cover the tampon bits.
*the plastic / not you.
Good luck.
.............
p.s: the plastic - it's a home made one of these. https://www.youtube.com/watch?v=XwBg8jQfjFE&t=1s
Clean around the seal with a piece of suitable plastic. (credit cards too thick / milk carton maybe too thin. Maybe an oil container? ).
If not too thick* you can carefully get it under the edge between fork leg and seal and clean out any muck that's causing the leak ... sometimes - if the leaks not too bad)
With a sharp blade, cut up a tampon to fit above seal / below dust cover.
Slide dust cover back down firmly to cover the tampon bits.
*the plastic / not you.

Good luck.
.............
p.s: the plastic - it's a home made one of these. https://www.youtube.com/watch?v=XwBg8jQfjFE&t=1s