How does one change the lubricating oil in a 3GM30? There is no drain
plug in the base.


Ignore the Loco character. He's an idiot. Buy a electric oil changing pump or
one of the small brass handheld units. They come with a hose designed to fit
down the dipstick hole. This will enable you to pump out most of the oil. Try
moving the hose around to get it to the back of the oil pan. You should be able
to get all but about a pint of the oil out, which is fine. Now add new oil
minus the pint and you're set.
If you're dealing with an oil contamination issue, you'll need to do at least 2
changes.

Good luck,

RB