I think all your problems are solvable. Lets take a look at the issues:
But my worst and most dangerous problem is the newer twist and stow rudder which is even more complex than the two previous generations of the rudder system and therefore less reliable. Because there was no way the up and down handles would move my rudder, I used to twist the rudder by hand and click in in the notch.Even with the paddles it was really hard to reach the shore and click the rudder in its notch again.
Your biggest problem is the easiest to fix. When the redder is down and locked, take the rudder down cord, pull it TIGHT and lock it in the "jamb" cleat highlighted here:
Just remember to unlock it before you raise the rudder. If the rudder hits something hard it will still kick up without hurting anything.
If you're having trouble operating the pull strings, you might be having excess binding on your rotating mechanism. Take an adjustable wrench or pliers and loosen the nut highlighted here very slightly
, so that the rudder pivots without binding but doesn't wobble in the housing.
Then you should be able to operate the rudder with the handles in the cockpit.
But then the steering handle came off....It took me quite a while to get the handle fixed, because it is difficult to find inch-measure screwdrivers in my part of the world (the Netherlands).
Hobie uses a liquid thread locker to keep those screws from backing out. Unfortunately they didn't realize this was a problem with the early boats. You can do the same. They use a product made by Henke called "Locktite Blue". Once you remove the screw, put a little on the end of the screw and this will glue it in place with enough force that it will not back out. You only need a small container. If your local hardware store doesn't carry it, you can get it on eBay. I use it on all my Hobie screws to make sure they stay in place.
To remove the screw, you need a very simple and inexpensive tool called an "Allen head" or "Hex" wrench. It looks like these:
The size you need is 1/8 inch (this not a metric size), and you normally buy these by the set for 5 to 10 dollars US. Again, if you can't find them locally, try eBay.
By the way, if this handle shows any sign of looseness or wobbling, it will be coming off soon. Fix it immediately with the Loctite before it becomes a problem.
The knob you can mount on the steering handle is nice, but by far not as nice as the steering part I made on the old Revo. I would make a new one for the Revo 11 if I could find inch screws that fit in the hole of the steering handle.
The attachment screw is 10/32 (S.A.E.) times whatever length you want; the knob end is 1/4 x 20. In both cases the first measurement is diameter and the second dimension is threads per inch. Here are some handles others have made:
Then, Holland can be pretty cold and in my Revo 11 I am having a problem that I never had in the other two: the water puddle you have to sit in after an encounter with a small speedboat or some such. Not nice I you are making a 5 hour tour!
With the Revo 11 this is always going to be a problem since you're sitting lower in the water. A lot of fishermen in the colder climates here use dry or waterproof pants.