well, what is the brand you are using?
the problem w/ ''tung oil'' is that theres a lot of things called tung oil
'real' tung oil (china) has a very sweet(?) smell and takes weeks/ months to tottally cure;
then the minwax stuff which is actually varnish that has been diluted so much to make it able to be wiped on and cure fast;
ive used it on necks too and ive had no big problems;
but if you did use one of these 'fake' oils, the problem might be that being varish, it just sits on the wood and wears instead of penetrating and sealing deep in the wood;
a good test for oil is to make a puddle in a dish and stick a tall cut off in it; leave it in there a day or so;
if it is oil; the oil will travel all the way up thru the grain to the top; and it wont harden for quite a while