05 rm250 powervalve question

I have notice the 90 degree breather take off that sits on top of a brass knurled fitting keeps coming adrift. I have used a little vht sealany to try and hold it in place but id rather replace properly sooner than bodge. the location (in front of cylinder head) makes it vunerable to crap which is why im even more keen to see it wont budge. is this a common problem (im thinking the 90 degree bit is worn rather than the brass insert) and does anyone have a part number. bike is 2005 rm 250 cheers