Piston rings are not problem, can be bought or taken from Chinese, with little revision. By the way - originally D4 had only one ring.
Chinese crank not fit - it is a bit another dimensions, and much worse in quality. Seems, more reasonable will be repair.
I will wait photos with curiosity!![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Chinese crank not fit - it is a bit another dimensions, and much worse in quality. Seems, more reasonable will be repair.
I will wait photos with curiosity!