I have repaired at least 3 dozen of these and fortunately they are one of the easiest of this type Umarex pistol to work on next to the 1911. I find a couple of things help, using a tiny dob of silicone glue or sticky grease to hold the trigger lock spring in place, and a piece of dental floss or cotton to hook the cylinder latch spring back in place after the pistol side plate is installed. A common fault on these I fix is straightening the zinc pressure plate after it is bent by over vigorous tightening.
Baz
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