Where did you find it, hull, transom?
West Marine sells a product called Gitrot that works well on small areas. I think you are going to find that the bad area is caused by water intrusion, not dry rotting.
2015 Seaark 1872 MV CC Etec-90
Two Helix 12 CHIRP SI's, , MinnKota Riptide ST80/i-pilot Link, Bob's Hydraulic
2018 Robalo R180 CC, Yamaha 115
Bitter Gun Owner