How can I repair a pressure sensing pipe on a Halstead boiler?

My Halstead boiler has a leak from what appears to be a silicon seal at the end of a pressure sensing pipe.

I'm just wondering if it is just standard silicon sealant or something else, a special silicon cap over the end?

I'm considering disconnecting the pipe as per instructions in the manual and just re-applying some silicon, replacing the pipe and allowing it to cure for 6 hours or so before, re-pressuring, does this sound right?

Would leave this to an engineer, but had one out who took a plumbers wrench to it, no idea why as it wouldn't be a tool you would use on the pipe. Think he was thinking ca, ching new boiler!!! I'm thinking not on your nelly for a bit of silicon!!