Gmood1, You would be better served using an oil/varnish type oil finish like Watco to rejuvenate the original oil finish as it would be closest to what the manufacturer used. The reason you have to use the "lemon oil" as frequently as you do is because it's nothing more than an oily petroleum distillate (no lemon oil at all) and it evaporates rather quickly. With a Watco type finish you'd only have to rejuvenate it every couple of years or so and you'd save time and money.
Jayboard's comments are solid and his suggestion to use tung oil will work nicely too.
Jayboard's comments are solid and his suggestion to use tung oil will work nicely too.