loud clunking noise when applying clutch

[EthanBart]

im not sure what has cause this to happen but most of the time i apply the clutch into any gear the car makes a loud clunk noise a couple of times,  any help is appreciated. I took my 1980 chrysler avenger to a local mechanic and he said its possibly a gear clash. I also have a small leak from the gearbox which he said looks like the rear seal and i could need a new clutch. Any help with these parts would be very appreciated. glass cover of left front head light, gearbox seals, clutch and a chrome drivers side mirror.