Hi. Well that taping method does work
, If viewed from above, the relative movement between adjacent boards fore and aft is the problem. If there is no tape, then you have three sides sticking, with movement, you could, and do, land up with two sides say left and bottom 'winning' over the right side and breaking its bond.
The method we use, (and if I was not so lazy I could do a youtube video)
Remove old caulking, clean, clean, and clean again.
Place masking tape over the slot centered well.
With a SHARP art knife, using the sides of the slot as the ruler, slice the tape both sides, and then push it to the bottom of the slot.
Now prime (if you are going to)
Gun the slot