.^^^
good vid.
If the wobble technique doesn't work I like the idea of the screw driver blades. I suppose you could use two feeler gage or shim sets.
Some good ideas there, but..........
There's nothing like having a tiny toddler helping you with the screwdriver tips.
"Okay what did you do with that tip, where is it?"
As the child collapses and turns blue.
Select to expand quotemkseven said..
& no need to use tape, make sure your mast is free from sand on rigging, difficult in sandy rigging spots that shovel the sand in there, double check it's properly together before downhaul but mostly dont leave your sail in shallow waters edge.
Sorry have to disagree. Not taping may work on some spots but it will get you in trouble at other spots. I have seen plenty of windsurfers who "never tape" come to my home spot, only to end up with seriously stuck masts. More than one of them has driven home with a 1-piece mast, despite lots of wiggling, 9 guys twisting, two booms, and whatever else they tried. The rigging is done on a parking lot behind some dunes, basically sand-free. The problem is sand in the water that gets into the mast, and then gets stuck when the water comes out at the joint. With 1-2 ft chop in 4-5 ft of water, we have lots of sand floating around on a windy day. With tape, there's never a problem. We usually use electrical tape instead of duct tape since it comes off better.
Coming from a very sandy place called - wait for it - Sandy Point, 
I have studdied this 'sand in the join' phenomenon for quite a few years. Well, since 2 piece masts appeared actually. 
I have found that these things aggravate the sand filling the join the most :
1. Letting sand get in the top part of the mast (Doh!) 
2. Not having a good mast plug in the top of the mast to seal it. Water flows downhill with gravity (now there is a revelation! 
) If water gets into the mast tip it carries the sand down into the joint. This appears to me to be the main cause of the problem, but it can still get in there in the absence of water.
Preventions:
1. Using a mast with the ferule in the top half facing down. Not common, but some RDM's are like this and it really helps because of #2 above.
2. Keeping sand out of the top part of the mast (Double Doh!)
3. Having a mast tip plug. And then, a good sealing mast tip plug.
4. Taping the join. This is not to stop sand getting in. This is to stop water getting in, and any water that gets in the mast flowing through back through the join and bringing sand in with it. Even if 2 and 3 are missing, 4 certainly helps a lot.
Just my observations.
PS. The same priciples apply to mast base extensions getting stuck in the mast. I try to never, ever let the bottom end of the mast even touch the ground when I am rigging!
PPS. I am a duct tape guy. I find it sticks better.
Ahh, Sandy Point! The only place I have had a mast extension firmly stuck in the mast from sand! If I ever go there again I will wrap everything in tape. The boom, the mast extension, my feet, everything.
In addition to the sand issue, I always tape to ensure no separation of the halves when rigging. You only have to break one mast to be a convert to that practice...
i prefer the Bear cloth tape from Bunnings as it tears off easily and is non-stretch
Excellent point Stretchy. And a taped mast is easy to pull from the luff when de-rigging in one go! 
If you loose your mast tip plug, and have no replacement, use either a wine cork, if that's to skinny, then use a champagne cork. Trim to fit snugly then cut off the round cork top. They actually work better than the plastic cap that comes with the mast.
Excellent tip Mastbender.
Althougn many sails nowdays have a Post/Pin type top that inserts into a recess in the mast tip cap.
A few more thoughts not explained in my video.
The tape is a nice tip but won't help with sand/salt/mud that's already there.
I like that the mast comes apart when derigging, I feel like it doesn't crinkle the sail as much.
The tip cap is a must because often times there'll be sand inside the luff sleeve!
Sometimes sand gets in the mast not only when we rig but also when we derig.
The wind can blow sand inside the mast when (de)rigging or simply leaving the mast out.
Ocean (resp. muddy) water can leave a salt (resp. mud) residue inside the mast.
No matter how careful we are, we'll all get our mast stuck sometime.
Fellas, my mast has a VERY tight fitting ferrule. It is two different brand masts grafted together. I had sanded the ferrule to MAKE it fit originally. Ive since sanded the high points as they were very visible once it all came apart.
As far as crinkling the sail when derigging. I tie a short loop of outhaul line to mast cap/ pin on sail. Spear a screwdriver thru loop n into the ground. Then twist n pull mast from luff sleeve. Undo the tape n separate mast. No crinkles no hassle. Happy days....
