There is such a thing as too much oil. Once the barrel is dry all you need is to run a patch lightly seasoned with oil down the bore. If you over-oil it a) it may not fire well when you load it and b) it attracts dust and grime to stick in the bore. You just want a light coating to protect from oxygen and humidity in the air.

What powder are you shooting? Your choice of solvent will depend on that. For 777 all I use is plain water. My Omega is about 6-7 years old and has a spotless bore.