You mention the grading outside is wrong, so it is a good idea to start by grading it properly, which means, sloping away from the foundation walls.
Check your gutters for clogs, clean them and, if you don't have them, by all means, have them installed. The downspouts should not be discharging too close to the house, but extended to discharge a few feet away.
You want to properly deal with the run off on the outside and keep the ground around the basement as dry as possible. That should improve the conditions in your basement.
Your basement leaks because the soil around it is saturated with water and the resulting hydrostatic pressure pushes water against the foundation wall, which, by following the path of less resistance, finds its way into the basement, usually in corners such as the one you mention.
All this outside work however, might not suffice to keep your basement dry, and you might need to improve foundation drainage by replacing the french drain outside, or installing an interior foundation drainage system.
Both types of foundation drainage work the same way: collecting water from the foundation. Here's some information about foundation drainage. Here's a comparison between different types of foundation drainage:
Waterproofing paints and sealants, just as you observed, will not work because they do nothing to relieve the hydrostatic pressure. Water is just temporarily trapped behind the coating, and with time and pressure, the coating bubbles, flakes or peels off.
It is in your best interest to have the drainage fixed with a cinder block wall, because the hydrostatic pressure might eventually cause them to bow and crack, compromising the structural integrity of the property.