Simply put during the 7 years they were made Abu just seemed to be obsessed with messing around with reels that were near perfect from the start, if they had paid more attention to plastics instead of internals then the reels would never of had exploding spools and cracking trip covers, had they not gone the silent A/R route then the coning issue would not of come around. Unlike other makes of reels washers and shims dont cut it on an Abu to get it fixed, you have to spend hours sometimes looking at parts and dating them to see if they match the serial number on the reel, simply put you cannot just put any part on a 78 model from a 79 one and the same goes for the 80-84 models.
In these photos you will see just how many changes were made in the 7 years of production
You can from the left the considerable size of the worm gear, its longer and requires the early rotor cup for it to fit through the hole.
Look at the main gear ends for handle attachment, on the left is the hideous first version 1977 main gear and handle which broke of if you put good pressure on when cranking a fish, this was changed in the same year.
The coning as I said can be many things, second hand reels from online scrap dealers are one of the biggest problems and the fact they sell any old part to a customer not understanding the reel at all is where it all stems from, if you study the photos you can see main gear changes, handle changes, coverplate changes, worm gear changes too, the one thing hard to see is the casting change made in the housings and until you understand the serial numbers you're onto a loser before you start to build a reel. I keep learning all the time but kind of have them worked out now. If anyone suffers this problem maybe this post will help or if you have any questions just ask, Im happy to help if I can
there is also the fact they have no idea which part is which, hopefully they will go away as quick as they turned up 
