I wonder if you can take a sample of the dripping water and have it tested to see if it is hard or soft? That would help narrow the problem. Is it possible to do this?
If it is hard, then you have a problem with the drain valve.
If it is soft, there are any number of causes, some of which are relatively easy to fix.
In the older units like yours, levels 2 and 3 were 'molded' together. If there is a small warp between the two, water will be short-cutting and seeping through or by-passing water ports. This would require this section to be replaced with separate levels (2 & 3).
Is your household water pressure less than 20psi?
Whatever you do, DON'T lubricate o-rings or seals with Vasoline or any other petroleum product.