So, you’be bought an old boat, or got a gearbox of Ebay, or traded it with a bloke in the pub. And it’s a Lister mechanical box, and it seems to be a bit stuck.
DO NOT try to force it into or out of gear! I have just sold a forward gear lever to someone who had one neatly sheared in two. There was no chance of the gear mechanism working as the forward clutch was completely rusted into it’s housing
If it is stuck, do some investigation, as my mate Wilf used to say ‘Don’t force it Phoebe’
The bloke with the sheared lever was lucky. When it broke, he didn’t break the gearbox cover!