Well, I've figured it out.
When I replaced the lower forestay section, I didn't have a choice on which end to connect to the jib block, I used the forked end as there was a swivel connected to the lower side of the block.
I was looking at the Hobie parts page for the H18 the other day and noticed the stock setup was with a swivel above the jib block only. When the wind was flat the other day, and the cat was on the beach, I stared up at my forestay hardware...mmm...I had a swivel above and below the jib block.
I removed the lower swivel, and all is well.
'79 H18 on Mallets Bay
Lake Cahmplain, VT
Dan in Vermont
Hobie 20 Miracle