New kitchen strainer leaking on Kohlr Cast-Iron sink

wysiwyg6000

I decided to be proactive and replace the existing strainer on it because it was starting to rust. I tried installing it the first time using a regular $10 kitchen strainer and liberal use of plumbers putty and had a small drip on the top left-hand corner of the drain circle. I think I either used too much putty or (more likely) the strainer started to turn as I was tightening it below, breaking the seal of the putty. So I tried again just now, starting from scratch, removing the old putty and putting new putty in (and less of it) and now it's leaking even worse! Do I have to use special putty or strainer basket because I have a cast iron sink? The whole in the sink is different than most other ones I've seen in instructional videos because it's not flat. The hole is sloped down into the sink at an angle, which I think is causing the problem. Do I have to buy the Kohler brand strainer that's like $30 for it to work on this kind of sink?

wysiwyg6000

Update: Ok, I used a lot more putty than the second time and I flattened it out when I applied it. So far, I've left it for an hour with about an inch or two of standing water and no drips have come yet. Ironically enough, I didn't tighten it as much as before and it seems to be working better (I think I tightened it too much and the rubber gasket was starting to get deformed). Am I in the clear after an hour of standing water? Is there a better torture test?

wysiwyg6000

I take it one step further and use a piece of regular white computer paper. The slightest drip on that wrinkles it nicely