Fork dust seals keep coarse dirt away from the inner tubes, but grit can collect behind their lips over time. Left there, it may lead to a leak at the oil seals deeper inside. After a muddy ride, look along both fork tubes for dirt or fresh traces of oil.
An adventure motorcycle owner’s manual treats cleaning the fork dust boots as a separate service task. Access involves supporting the motorcycle securely and removing some surrounding parts; the procedure can differ by model. Without suitable stands or experience, a workshop is the sensible place for that work.
Keep oil and cleaning products off the brake discs: contamination reduces braking performance. If oil returns to a fork tube after its surface has been wiped, cleaning alone has not resolved the problem. Have the seals inspected before riding again.