Taz,
Had this happen once. The base pin latch was not getting a good bite in the notch toward the front of the base pin.
To verify if this is the case, do the following:
Carefully note the positon of the latch while the base pin is in the normal position in the gun.
Now, remove the ejector housing (1 screw) so that the base pin can be completely removed. When the base pin is all the way out of the gun, does the latch go farther into the frame? You'll be able to see how the latch should go all the way across the notch in the pin. Odds are that it can't because the notch in the pin is too shallow, or is not cut at exactly the right angle.
It is probably not worth the trouble and expense to send back to Ruger, in my opinion. If you can determine that this is the problem, then get a small round file and open the base pin notch bit by bit till the latch can close across it fully. You can 'paint' the base pin with a laundry marker or similar to try and figure out where the latch touches and metal needs to be removed.
Sounds complicated but if this is the problem, maybe a half hour job if you have the tools at hand.
You can also get aftermarket base pins from Belt Mountain. They are very good quality and about 20 bucks or so.