Galco, DeSantis and some other holster makers specifically say to NOT use any oils, softeners, saddle soap, etc on the leather ... it can relax the fit, making it too loose for proper retention.
The baggie method works OK, wearing it will also help to get the holster in form.
I had a new (not Galco) holster that was so tight I had to literally put a foot on each belt ear and pull to get it out (obviously "not ready for prime time").
After a couple days of working the gun in the holster (with and without a baggie), wearing it around the house, and just leaving the gun in the holster in the safe overnight loosened it up. Now it's just right; it's easy enough to draw but still has great retention.
I know it's hard to wait, but if you take the time to break it in right, you'll be much happier with it. That is one of the advantages of leather (over Kydex or similar); it forms to you and gets more comfortable over time.