You really need re-soldering all of the joints.
From your photo and what you mentioned, looks like you only re-soldered very limited number of joints in the past.

As Heineken mentioned above, you are looking for the hair line crack.



This is one example.
As you already opened the FCU, you will know how far this photo was enlarged compared to the actual size of the soldering pad.
Arrows show some of the cracked joints.
In fact almost all of the joints in this photo are cracked.







Almost all of your photo are out of focus and not high enough resolution so hard to tell but even so, there are many suspicious joints.
This is from your 4th photo.

Circled ones very likely to be cracked, arrows are suspicious but hard to tell.


Kaz