2046W Tender Whistle - Classic Toy Trains Magazine

Another issue related to an older set I hoped to use this year at the holidays.  The set with the 2400 cars is headed by a 671 turbine.  I went to see if the tender worked yesterday and it made a low wheezing noise.  I believe this is referred to as the 2046 tender - streamlined plastic body, 6 wheel trucks, Pennsylvania stamped on the side. 

I went through it -- cleaning, a little oil on the wick, etc. -- and now it whistles like a champ but the problem is it just keeps whistling.  The relay stays closed, in other words.  Not sure what is going on.  I run TMCC and my other newer and postwar locos do not suffer this issue, so I don't think it a control issue.  I have tried to keep all oil off the relay, and even went over it lightly with compressed air from a can.  No luck.  Tapping the tender shell will generally result in the relay releasing.  Any thoughts?  Thank you again in advance.