Dometic Toilets

Does anyone else have trouble with the Dometic toilet flap opening and shutting being excessively difficult to  operate and iff so is there any known remedy,have tried the usual with silicon grease and it solves the problem temporarily and then it’s just as difficult.
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Ps it’s a 2017 symbol

The slide on mine stiffened after a while and was very difficult to operate. I thought it was the flap on the cassette at first, but soon realised it was the slider on the front of the toilet.

A liberal spray with silicon spray loosened it last year and it's been fine since.