I know the plane this engine is in, it has a pretty good cooling setup. With experience on "a very similar brandname and source" of engines, It is more than likely an air leak. That might not be a serial number provided with it - it is a coded "use by" date.

Hey Doug. No, I left TEDA a year or so ago. Still go back from time to time (well - to Xian Shui Gu mostly) to "catch up" with some people. The place has changed a lot but the Wei Ha is still there