Here's the 315 I got several weeks ago in a large lot. Very nice engine, low run time, with the air chime whistle in the tender, and it works.
I agree about the 710 controller, it gives you a better sound than just the normal buzz from the 708 air chime controllers.I won a 315 on eBay that looks kinda dusty and the seller listed it as "untested". It also came with an original but unmarked wrapper. This was one of those rare engines that a repairman loves to find as I don't believe that this engine was ever worked on. Every part was original down to the motor brushes. My guess was that it was bought as a Christmas present and run a little and them stored away in a duty dry place for all these years. All I needed to do was a complete disassemble, scrape all the old hardened grease out of the gears then re-lube everything. Needed about a dropper full of smoke fluid to saturate the dried out wick and it ran and smoked great! The air chime speaker also worked good giving out that loud buzzer sound. At least with my 710 controller I'm able to wary it some for a better effect.