Macdee flushing system?

I have a Macdee flushing system.. hydraulic with long thin plastic pipe. Concealed in vitreous cistern.
It has one flush silver button on front.
It has yards of this plastic pipei inside and it is often slow to let the button out or wont let it out at all.
I have found that the cover on the installation has to be ajar to allow anything to happen at all!
I have been on the Macdee site but all the tech help telephone numbers give ceased line noise!

Flush button gets a new lease of life every so often and works ok for a day or so.

Any ideas please?

Rosie