You really can't do serious damage to a manual, unless you're jamming gears all the time. A manual tranny is just a bunch of old fashioned gears that can be filled with 30 weight once and then pretty much forgotten about, and the only brunt of stress and possible failure is the clutch. There is no need to worry if there is oil circulation or not, because the oil only circulates when the gears are moving, and doesn't need forced circulation, unlike an automatic, which has vaccum lines, and a hydraulic torque converter. Coasting in neutral with a manual will do no more damage than driving in fifth gear. Coasting in neutral with an automatic can cause vaccum and ecm problems. Especially now with computer controlled trannies which use speed and engine rpm inputs to optimize performance and efficiency. The computer may tell the transmission to do things it can't do when it's in neutral.