It sounds in my experience that all the linkages ( including the handle orifices) need cleaning and freeing of rust and grime and then possibly a light lubricant (vaseline) thinly applying to them. Also check that the siphon is moving up and down freely and is not being impeded. It maybe the last time you removed the cover and attempted repairs you disturbed something. Check all around.
Maybe this time when you replace the cover, carefully drill through the relevant tiles and fix on top of the tile therefore not having to smash them to get them off. You can get screws with white tops, which dont look to unattractive.
Bucket head.
December 2010