In article <5gqhkm$4v5@nntp.Stanford.EDU>, philduke@leland.stanford.edu says...

>I was looking a used Nikkor lens the other day which was mint except for
>what appeared to be oil traces on the diaphragm segments (sorry, I don't
>know the consacred name). The dealer, good guy, told me to avoid it. Now
>I am wondering if I should make an offer for the lens as is... What is
>current wisdom about oil on diaphragm. User fixable? Expensive repair by
>Nikon only? Let it go? Thanks in advance for advice.

Oil on the diaphragm is unusual for Nikkors, with one notable exception:
the 55mm f2.8 Micro-Nikkor - EVERY ONE of them that I have had a long-term
acquaintance with (and many others, which were caught while in the O.O.T.D.
condition.... ;-) has developed "O.O.T.D." I have seen only a couple of other Nikkors with the condition. If the spring tension is strong on the lens
you looked at, and there is no hint of diaphragm blade slowness when
hand-operating the small diaphragm actuator lever on the rear of the lens
(with the lens set at minimum aperture), it might be OK to buy (if discounted).
(Nikon servicing for "O.O.T.D." is about $80 in the US, as I recall...)
I have fixed one of my lenses with the dreaded "O.O.T.D.", but I don't think
I recommend trying it without some experience...
Hope This Helps