Some advice please.

I had just finished off getting my Vivacity 20 yacht ready for the
coming season when I made a rather alarming discovery (that's sailing
for you: a succession of alarming discoveries interspersed with the
occasional sail!). I noticed a large crack in the arched beam that
runs under the foredeck around the bend where it dips to run under the
port side deck.. The beam is presumably intended as a support for the
deck-stepped mast. On investigation, I noticed that this had been
previously filled (with silicone!) and painted over by a previous
owner. I bought the boat last year and sailed all last season without
any obvious problems, and for all I know the crack may have been there
for years before I bought the boat. On probing the crack, which runs
all the way around, I found there was solid material beneath (i.e. the
beam does not appear to have broken all the way through). I am
wondering whether all that has happened is that the GRP that sheathes
the beam has cracked and whether I need to worry about structural
integrity? Why has the crack reopened? Has this been caused by mast
compression (maybe overtightened shrouds)? I intend to fill the crack
with a good epoxy product: will this be sufficient, or do I need to
investigate more radical solutions?

These old Russell Marine boats were built pretty chunkily, so I'm
hoping that I don't need to embark on major repairs or adaptions.