Worst case is that your right crank seal is letting some leak in and its burning off slowly out the pipe.
But look for leaks around the clutch cover gasket.
Also check your coolant to see if its milky.
Do a quick leak down too.
JB sounds good to me.
Hell if it don't work i have a stock petcock on the bench i will give you.
I use a dual Pingle so i don't need the other one.
Let us know how it goes.
Put the steels in so the notches are evenly distributed around the basket/inner hub. Its like ever 14 degrees for them.
Think there are marks for them on the stock basket also.
If they don't look like total shit and are not gouged to dog shit, well then try some http://www.partsforatvs.com/default.asp?p=537&c=356&cn=Z400 and stay outa the mud.
Post a big pic up close so i can see.
Next step would be wet sanding.
http://www.mooseracing.com/catalog.jsp?level1=1756&level2=1783&level3=1822&product_group_id=7458
I run these with my 35's and box.
Work well.
Part# 1050-0054
Vendors on here can get you the same ones also.
OEM exhaust springs are the only;y type i will ever run.
They cost a lil more then the shitty after market ones, but are Much better and last a long time and don't fall off out of the blue.
My opinion anyways.