Leningrad rangefinder coupler problem

Hi all,
I just received my leningrad, I haven't done much test about in but I've already encountered one major problem. The rangefinder coupler doesn't spring back, it just stay in whatever last position it was. any way to fix this?

any help will be greatly appreciated

Easy Kievan 81 Just spray a little os WD 40 oe similar lub in the axle of the rf
Regards
LP

the picture

Didn't seem to work. It isn't stiff but it feels like the spring(if any) is broken.

I lube it from the mount, I haven't open the top yet...

I spoke too soon, it work! Just need to loosen the big screw and make sure the lube sip in the screw hole.