1999 Mitsubishi Diamante Shakes and wobbles especially on I

Hi:
I'd like to answer your question, but I don't understand what you are asking. So, I am going to take a shot in the dark and provide the following details. Approximately 6 weeks ago I began to have a problem with the above car shaking & wobbling. It was more noticeable on the back end. I took it in for an alignment and I found out the back tires were worn (on the inside down to the steel belt). I was quite surprised about this as the tires were newly purchased less than 1 year ago. So, I had the car aligned and put new tires on. Same problem reoccurred on the back tires, so I changed the back tires again. This time the tire technician told me there is something wrong with the bushings (?) In the rear wheels and that the back end is way off. So far in fact, that they couldn't get the back to align correctly. He further stated the part that I need to correct this problem cost $1800 (not including labor). My car is a 1999 with 200K miles, and although I love this car (and it's the 1st major problem I've had with it) I do not want to invest this much money. Since I've had the car aligned and tires changes, the shaking is less. However, when I pick up speed (55 miles/hour or more, or drive on a wet or icy surface), go over bumpy road surface the back end begins to slide. The car seems to slide more to the left now, where as before the entire back end fishtailed and it was difficult to maintain control.
Any help/suggestion/advice you offer will be greatly appreciated.

Thanks so much. The diagram really helps. Nope, they told me $1800 just for the part. I told them to FORGET it! You are right, I love this car, but it's not worth putting that much money into.

God bless you and again, thank you. May you act of kindness be returned to you a hundred fold.

OK I also have the same problem by the only difference is that my car just crossed 100k miles its doing the same wear of tire on the inside and when I took it for alignment they said they cant do it as it has maxed out on that part which is moved to align or it has maxed out on that adjustment not teh problem is that some of the shops I took it to are saying its the struts if I get them replaced that should fix the problem , some are not sure as they do not see any thing bent , one shop says struts wont help although the car is sagging from the rare and when it goes over a jump the rear tires wobble a bit, and one can feel the left and right movement of the rear end, one shop even told me the knuckles could be bent and that replacing them should solve the problem now I am compleatly confused on what to get fixed as the experts them self are not sure whats wrong

Thanks for your reply, but will this solve the problem as they too at the shop are not sure if the knuckles are bent , and will changing the struts straighten up the wheels as they are a little tilted toward the inside, I mean the top of the tire is tilted toward the inside, on the alignment reading it shows something like -2 degrees almost on both sides, one is -1.7, and will only changing the struts remove the sag