85 mercury 25xd shift issue

[rigoletsfishnfinatic]

with engine running it makes a fast paced ticking noise when trying to shift into reverse like its close to engaging but won't.pulled lower unit when shift rod is pulled it goes into reverse but pops out with one full revolution of the prop by hand .i did notice i was missing the shift rod washer at the top of the shift rod.the control cables are probably original but look great although the cams and linkage i know must be worn some its a 85