This is a simple mechanism, in which anyone with a bit of methodical measurement/comparison could diagnose the cause of the reported problem, with ease.
With all due respect, several people (e.g. Guy ggggr) have made solid suggestions and/or observations, which you seem to just ignore, preferring instead to post more pictures and questions.
Perhaps you should take the gun to an airgunsmith, or see if a knowledgeable/experienced member lives near enough and would be willing to help you out.
Happy Shooting!! Paul.
"We cannot solve our problems with the same thinking that we used when we created them" - Albert Einstein.