I have managed to break 3 of the slides on the foot of my 1990 E34 mainsail twice in the first year of ownership. The first time I and my sailmaker assumed it was the age of the plastic. But now the new ones have broken so I don't have that excuse. I have not sailed in anything over 20 knots so the sail has not seen a lot of force. The slides that break are in the middle of the foot. Is this from too much downward force on the main sheet? I haven't overtightened that I know of. Unfortunately I have not seen them break but only noticed later so I don't know the conditions that caused the break. Any ideas or experience with this?