Hot water mixing valve 550 leaks at plastic connectors

Sagiller

We are having trouble with leaks at the plastic screw-on connectors on our water mixing valve.  The hot water supply side has a slow leak (red Pyrex tube) and the mixed water outflow side has a bigger leak (white braided tube). The purge screw is totally tight and isn’t the source of the drips.

We tried putting some Teflon tape on the male part of the thread/nut junctions but that didn’t help.

So today we took the valve apart.  There doesn’t seem to be any washer inside the three nuts, only what looks like some sort of silicon compound that was put on the end of the brass fittings and might act as a washer. That silicon seems a bit ragged.

Does anyone have any thoughts on what this compound is? And how we might replace it?

Also, we see there is a new version of this valve which uses compression fittings.  Is there any thought on us replacing this older valve with the new one?  I realize we would need to replace the plastic connectors from the hoses onto the new valve.  Has anyone done that?