Thanks for all the interests on the post. Two issues have been emerged.
The first one is on the tire itself, whether it itself lasts or not. As mentioned earlier in my posts, I had used Yokohama AVS Sports tires on all 4 wheels. I was fully aware that these tires didn't last, but please note that the 2 at the front had actually lasted 22,000 km, while the pair at the back only 5,000km! These were the comparison I was drawing, not against other makes. I have had 10 over vehicles, both Japanese and Continental cars of 2,000cc or above and I had never had any problem of premature tire wear like this. So, that led to the second issue.
The second issue lies on the mechanics of the wheels, suspension, linkages, etc., etc. of this particular w124 I am having. As said, I have changed the springs, shock absorbers and have done the wheel alignment but still to no avail. Having seriously thought of the problem, I tend to suspect it was still the wheel alignment problem that is the culprit. Now I re-call, it might be that the mechanic has used the wrong data set when he did the wheel alignment for me sometime ago. I was there when he did the wheel alignment and he did indicated that he was not too sure which set of data to use. So, he could have picked up the wrong set just to do the job for me.
So, I am going to send the car to another workshop these few days .....
1987 W124 300E Auto right-hand drive