Diff Whine and Leaking Plug

[JHMC51]

Hi guru's. Firstly, my ZD30 GUII has a rear diff whine above 80k's, barely there under load, noisiest on a trailing throttle and just there backing off. Would a diff rebuild be enough or would I be better doing an exchange/new one?
Secondly, I have an oil weep from the front of my engine which appears to be coming from a square drive plug near the crankshaft pulley. Is this the oil pressure relief valve? My manual isn't real clear. Could I take it out, apply some thread sealer (liquid) and replace it without upsetting the oil pressure?:cheers:

Thanx in advance

[megatexture]

my diff was whining in my hilux and soon after my ring and pinion shattered and punched a hole in the diff housing.i had to replace the whole lot, id prob look at it sooner than later as a precaution i was lucky enough to get it covered by warranty if not was going to set me back about 3k
cant help you with the leak good luck