Both levers on my older style(with indicators) would not return.
So I cracked them open and took a look into the scary depths….
They are not too bad actually as most of the innards are held together and can be removed as one lump.
What I found was that the largest(bottom) clock spring had some coils overlapping and the pivot bush in the metal lever was binding on the pivot bolt.
Once these two problems were sorted & the shifters back together(Do not over-tighten the central pivot bolt!)they work as new.

Fettle on….

I opened up some X9 ones once, took me over week to get them back together. I had to do loads of googling and print out pictures and fiddle in the man cave late into the night several evenings in a row.

The bike shop I spoke to laughed and recommended buying new ones as they couldnt fix them.

The X7s on my current bike are a little eaiser though.