Which bit is leaking? If it's a thread have you tried PTFE tape? You'll need about 10 wraps of it for it to work properly.
It's leaking from the threaded bit....tried PTFE tape and plumbers sealant......I've tried to use all sorts of rubber washers too to no avail.....
I'm pretty sure PTFE tape would seal it Daz, I have plumbing experience. You need a lot of wraps on it, best way to describe it would be enough so that it looks like too much, like you'll not get the nut back on. Other than that, I suspect the part could be broken, like fractured in which case you'll not fix it.