Fuel in Oil

[Steve Sherman]

Hope this isn't a repost, my subscription failed before and I don't
think this got in....

In doing a routine oil level check in our 87 5KTQW, I noticed that the
oil smelled of fuel (gas) rather strongly.  Other than running rich, is
there anything else that could be leaking gas into the oil?

Can I adjust the mixture myself,, and if so any tips on how to go about
that?  Anything else worth checking out for this?

TIA