Sef,
I had a similar problem on my C30 & my new main several years back.
Here's a simple fix pal.
Drill-n-tap your mast 1" above the top of the slot opening with a 1/4-20 threaded hex head bolt-n-washer. If the track is too narrow for this, drill your hole near the top of your slot with a washer that fits & will not allow the slide to pass by. Be careful that the tap is threaded properly.
I use a 1" long S.S. bolt & oversize washer in my track. Remember not to over tighten the bolt so as to avoid stripping the threads (this is where the Never Seize or Lock tight comes into play). Position your hole so that the oversize washer will bottom flat across the track when tightened or if in the slot, the washer is sized to not allow the slides to pass. Coat the threads also because you are working with dissimilar metals. This is called Galvanic Corrosion & S.S. will corrode aluminum over time if not sealed and/or coated properly. This can also quicken when in a salt air environment.
https://en.wikipedia.org/wiki/Galvanic_corrosion
At times, you will remove & replace this bolt/washer when taking off & putting on your main.
I have also done this for friends on their boats & now, nobody drops slides unless they want to.
Just my opinion if you want an easy project & a simple fix without the grief pal.
CR