RE: getting the mast extension shim out of the mast
What is the shim made of...?
Aluminum, or plastic?
Is the shim "split" down one side...?
If not, once you get it out of the mast, it would be a good idea to take a hack saw and split it. Then it will "collapse" a little and should be much easier to get in and out of your mast.
Did the extensoin have a cap or a "keeper" at the top to pull the shim back out?
Often, if there is a rubber pin or an spring type "keeper" you can put the extensiion back in and keep rotating it around and pulling out gently to free the shim.
If not, the best thing you can do it make up a little too.
Use an old scredriver with a long shank or perhaps a piece of metal pipe about 1/4 " smaller that the ID of the shim.
Cut a notch on one side near the end with a flat surface so you can get the flat surface of the notch up past the shim and "hook" the top end of the shim. The tip the pipe or tubing so that the notch really "engages the top end of your shim.
Pull sharply out the end of the mast and the shim should dislodge and come out.
If you know anyone with a small "slide hammer" type den puller you could make a steel disc to screw onto the end of the slide hammer that just fits (maybe 1/32" smaller than the ID of the shim) inside the shim, and use that to tap the shim out.
Then split the shim and if it aluminum, collapse it very slightly so it grabs the extension, not the inside of the mast.
Hope this helps,