I am a furniture builder and over the last 25 years I have used and experimented with nearly every coatings system I could find a use for. Beretta uses tru-oil in your gun's case. When using oil finishes I have found the best results come from tung oil-based varnishes that require multiple coats. You ultimately have two options in my professional opinion: recoat several times with tru-oil or have the stock refinished. Recoating is a snap if you have time: lightly sand with 320 sand paper, wipe down with acetone, apply tru-oil with a rag, let dry (in a low humidity environment) for 2 days, buff the glossy film off with 00 or 000 steel wool, and repeat 5 or 6 times (without the acetone). A deeper, more beautiful finish will appear if you coat it 10 or 12 times. Use paste wax occasionally and buff for decades of use (as often as a church-goer might polish their leather shoes). Do not put wax on it the way it is now because of the old rule that "you can put wax on oil but you can not put oil on wax."
A little more on option two: The highest quality results that I have achieved or seen on other's fine work are finish systems that use an epoxy sealer, and then are top-coated with a premium varnish. Excellent finishes take time, expensive equipment, or both. The amount of money that you spend will be commiserate with the quality of end product that you receive. On the bright side: If refinishing the stock, you have a great opportunity to make any fitting adjustments and to recut or deepen the checkering.
