Eljer gasket misfits

My wife and I bought a new Eljer Patriot 17" bowl this weekend and have been trying to install it with our existing American Standard tank. However, no gasket we have tried works just right. It seals and there is no leak, but the tank wobbles incessantly. Any ideas?

Using a 9/16 gasket.

Toilets are very much manufactured as a "set". Plumbers will never recommend to put a bowl of one brand together with a tank from another brand. Even within a brand, not all models are compatible for the "mix and match". To further compound the situation, if one of your pieces is pre-1.6 gallon ( approx. 1992) likely it would not fit any new parts, and if it did, there would be flushing problems.

Where did you buy these? If any plumbing store or even a box store sold this combo to you, I would go back and raise the dickens with the manager. This is a mistake even a rookie should not make.

Rookies

The rookies would be us. We bought the bowl without consulting anyone assuming things were plug-n-play. (My wife had done this before but only with old equipment at her parents' house.)

So back to Home Despot to buy the tank. 12 hours of work; five trips to the store; and one endorsement to let a professional handle this #%@!