Sony TC-399 idler slow engaging with captain

[ppppenguin]

I don't know the specific machine but hardened grease is where I'd look. Presumably there's a solenoid and mechanical linkage pulling the idler. Look for signs of congealed grease on the moving parts. You may be able to clean them in situ with isopropyl alchohol, white spirit or petrol. Be aware that the latter 2 are very bad for anything made of rubber.