This was a few years before my time, but as I understood it he wanted to leave Widnes and join Wigan but Widnes would not sell him directly to Wigan.

Probably down to knee reconstruction (iirc) in the late 80's, which blunted his pace. Possibly, we could've given him a run in the second row. One of the game's biggest wingers, and regularly "took the ball up", in a set of 6, and never shirked work. Imagine his effectiveness, running into a well timed pass from his scrum half.

His resulting 2nd testimonial was down to the club's long standing problem of lack of ruthlessness.

Define decline

A gradual and continuous loss of strength, numbers, quality, or value. For example, 'Mark Forster's misjudged attempt into conquering the sports retail market failed due to a decline in sales'

I see why you couldn't answer the other one now

My take on Charnley is that we're simply not playing him in the same way as we did when he first arrived and when he was scoring trieds for fun - at least that's my theory.
The problem is I can't define exactly what way we were playing him and what went up to make that difference to how he is now.
I know SP likes to use the wingers to take the ball up but so do many other coaches.