Steve,
I've never had this situation (locking mechanism 'gunked' up) but I've gone
through several cars with 'improper keys' and a need to
refresh or replace the steering/ignition lock mechanism.
Usually when these type of locks wear, they get easier to turn
and a surprising number of other Datsun keys will work them.
Even if you are sure one of the keys is
correct, it wouldn't hurt to remove the lock assembly for
cleaning/maintenance. The electrical switch at back of lock
is easy to remove and test but it should never be the cause to
not turn - yet this is worth checking first.
Otherwise, assuming this is a pre-74 Datsun and if you are comfortable with this:
1. Remove all steering column shrouding.
2. Remove ignition key/lock mechanism. *
3. Disassemble to force lube into shaft and lock bits.
4. Tap lock shaft to free up and/or work key well into lock.
* For second item, you'll need a Dremel tool with a thin/sturdy cut-off disk to make slots on the anchor bolt heads which do not already have a Phillips head inset. Then a straight-slot screw driver can be used to remove those bolts.
To quote Lou C - this is a 'one beer job' -
but you will need the cut-off disk. Highly valuable to to have
in your tool kit.
Also, once removed, it's always much more cost effective to take the lock to the locksmith, than the other way around.
BTW, I've been advised by a trusted
locksmith friend to avoid graphite, silicon, or other 'specialty
lubes' and start with WD-40. They say graphite is their friend
as users tend to apply more than needed and when that does not
work, they apply even more, thus making it worse to the point
they that need the locksmith - who spends time flushing out all
the graphite before being able to work the lock. YMMV.
Paolo_____
Paolo (Paul) Musante, MS PE