clutch slip vs knackered gear box

whats the difference? :ermm: how does one ‘feel’ vs the other? if you know what i mean

A knackered gear box will manifest itself in a number of different ways- inability/difficulty selecting gears, popping out of gear under load etc. whereas a slipping clutch will let the engine rev without a corresponding increase in road speed particularly under load, I can’t think of anyway a gearbox problem (other than popping out of gear in which case the engine will rev freely as in neutral) that will do the same thing.