1996 E320 53k KM, 722.509 transmission, suddenly hard shifting

[softtouch]

My 1996 E320 has 53k km when the transmission started to shift very hard from 1-2-3-4, but not from 4-3-2.

The transmission is 722.509

It did not happen over time.

I drove the car, everything was fine as usual. Parked and turned engine off.
Later that day, had to use the car, started and it had this hard shifting.
I brought it to a shop.
On the bill ($400) was:
Replace valve body piston seal kit
Valve body seal kit
100% ATF replacement

It did not solve the problem at all.

Now they want to overhaul the transmission, lineup etc. I still cannot believe that this is needed after just 53k km.

Strange is, the transmission was 100% perfect and very smooth as I turned off the car. Then after turning on, transmission was bad (must be a ghost playing with the transmission during the time the car was not used).

Note that I am living in the Philippines, here's no Mercedes service. I found a Mercedes mechanics who worked for Mercedes here before, as we had still a Mercedes service here on the island. But I smell that he just want to make some extra money with a maybe simple and cheap repair. And with an overhaul, he would make a lot of money ($1600)...

So, I would be grateful for ANY suggestion about this issue.