I'm replacing a toilet cistern. The old one is an annoying size, new one has the same screw holes just a newer model.

When I took the old cistern out out it had a bunch of silicone on the back, presumably to help hold it to the wall. I've cleaned the wall and repainted. The two outer screw holes had hollow wall anchors that I left in place and will reuse, the two inner ones the anchors were coming out so I replaced them with two part builders fill which is extremely dense / hard. I'll drill holes into the fill then screw into them.

As well as the four screws, should I put some silicone onto the back of the new cistern to help hold it in place? I have some Selleys 3 in 1 fill / adhesive. Or is it a waste of time that will just make future maintenance more difficult?