Damp basement wall - How does the water penetrate?

Hello dear forum
we have bought a house from 1980 and found that with a sharply rising groundwater level, water enters in two to three places in the area where the basement floor and wall meet, which shows itself through damp walls.
As I see it, the basement floor and the wall were poured up to a height of about 1.5m. Only after that was masonry done.
From the outside, a black sealing (as thin as paint) can be seen on the sand-lime brick, which, I hope, reaches down to the foundation.
This summer I want to tackle the sealing of the house walls and completely renew it.
Now my general question. How can water penetrate into the interior in the area where floor and wall (which appear to be poured as one, at least it looks like that) meet?
I am an amateur and eager to do it myself and appreciate any help!
Best regards

It is by no means unusual for moisture to penetrate after 40 years. The coating, whatever kind it is, ages as well. You will have to dig around the entire perimeter and reseal the wall from the outside. There are various systems of coatings, membranes, and the like for this. I would get information and advice from the local building materials supplier. And once everything is open, I would also lay a drainage pipe in as well.

Additionally, it should be noted that it has proven effective to do this page by page and not to expose all directions at once down to the foundation (especially not too deep). Otherwise, you may have other problems besides a damp basement.

Excavate by the page and seal from the outside, lay drainage. Possibly also use an injection system to make the walls themselves less permeable.

Possibly also make the walls themselves less permeable with an injection system.

Injection is not suitable for pressing moisture but for rising damp! However, when opening sidewise, the effort to measure the drainage is higher.

Would you then apply a bituminous waterproofing on the inside of the base slab? Or not treat the base slab at all? And would you additionally seal horizontally above ground level (cut and injection) to prevent the capillary rise of moisture into the ground floor walls? I had a project like this a while ago and wasn't sure how to handle it... In the end, I didn’t have to make a decision.