At the end of January 1935, a Kychap double blastpipe and chimney was fitted to the W1, which eventually required the fitting of a smoke lifting cowl for better smoke clearance. On August 21, 1935. 10000 was returned to Darlington for the last time in its original form, having covered another 20,823 miles since June 1934. 10000 had proved to be extremely capable, but it was also unreliable, as out of the 1,888 days in service, the locomotive spent 1,105 at Darlington Works alone.