If you open up that top and you have a big or little split in the rubber diaphram then you have the option of just putting it back with a good one...
if your if that is not your problem then you will need to deal with the rest of the stuff...
Mine was fixed in my 1980 240 by just putting in the diaphram...

Did you do a search ? There is a LOT of good info about this.... and I know I have posted pictures of mine being fixed....