Shoebox joint leak on a Mark 1

Jan 4, 2015
3
Catalina 30 MK1 Lahave River
Hello all, My 78 is now not leaking any rain water as Ive rebedded everything however when heeled to port water comes in at the hull/deck joint. I know I must remove the rubrail and am hoping for tips or advice on how to go about resealing and which product is recommended for this application.
Thanks in advance
Peter:D