No experience with the Dual 505-3. But if I were in your position, I'd probably be inclined to replace the stylus on the current cartridge. It would be the easiest solution. And also cheaper--the OM10 stylus at Garage-A-Records is about half the price of a new Red cartridge. Plus, I don't know what was originally used by the 505, but the OM series would be closer to original.
Normally, I would not go with the OM40 stylus--it does seem like overkill for a budget turntable. Although, the price you can get does make it very attractive. For less than a new Blue cartridge, you'd get a stylus that's much BETTER than the Blue.
I hope you enjoy the 505--it was, as I recall, considered the best budget turntable in some circles once. A cheap 503 which I bought to play with has--frankly--amazed me.
Normally, I would not go with the OM40 stylus--it does seem like overkill for a budget turntable. Although, the price you can get does make it very attractive. For less than a new Blue cartridge, you'd get a stylus that's much BETTER than the Blue.
I hope you enjoy the 505--it was, as I recall, considered the best budget turntable in some circles once. A cheap 503 which I bought to play with has--frankly--amazed me.