Toilet Tank, rubber plug won't seat

My toilet's tank, there's that rubber bulb that you lift by a chain when you push the handle, and when the air filled plastic ball rises high enough with the water level, that rubber bulb sits back in the drain of the tank. Recently the water in the tank ran and ran and ran.... I found that the rubber bult wouldn't seat, but if I gave it a bit of a push with my finger, stick, or whatever, it slip into place, water began to fill tank again, and plaster ball rose, and water stopped runnning. But it continued to be a problem. Upon checking it out, everything seemed in place and working. The chain was in place, the handle or lever worked properly. The only problem was that the rubber bulb wouldn't seat. I checked where it's attached to this stem or whatever, and on both sides, the rubber bulb was broken, detached. When I checked the rubber bult itself, I realized a black gook-like grease all over the rubber bulb. At first I thought that shouldn't be there, so I wiped the grease off as best I could. Then the rubber bulb was harder to seat when I used my dull stick to push the rubber bulb into place. I think the black gook-like grease was to facilitate the seating of the bulb. Anyway, the problems seems to be that where the rubber bulb sinks into its seat, right at 12 oclock--if the bult was up and down on a diagram--the bult just isn't getting past the lip of the porclean tank's drain. I now think the grease was to facilitate this process, and since I wiped the grease off, it's even more difficult for the bulb to seat correctly. My point is this: (1) why in the first place did this rubber bulb begin to have problems seating, i.e. the end of it catching on the porclean tank's drain preventing it to seat properly, (2) was it the grease and that over time, instead of wiping the grease off, I should've applied more, and then the bulb would've seated correctly again, and (3) now that I've wiped the grease off, I've only added to the problem.
If I'm correct, can this problem with rubber bult be solved by buying whatever black gook-like grease plummers use to help seat the rubber bult in a toilet tank? Or, since I've added insult to injury by wiping the grease away, and now I see a black mark on the lip or edge of the porclean toilet drain where the bult seats, where it's edge meets the drain, passes and seats, but is this black mark and indication that damage is done to the rubber bult or that the porclean drain may have to be cleaned, and the black goob-like grease applie to the rubber bult, before I can resolve this problem, or, finally, (3) because of the afore mentioned insults to injury, lack of knowledge, whatever, will I have to replace the rubber bulb becuase, since the grease was removed, now the bulb is worn un-evenly in that area where it rubbed against the porclean toilet tank's drain, so in effect, I'll have to clean off the porclean drain, that black stuff that's accumulated, and replace the worn or damaged rubber bulb?
OR! Am I completely wrong with any of my assumptions above, and I should just call a plummer?
*Running out of solutions, please help. Even, please e-mail your reply to snipped-for-privacy@hotmail.com. Surely will be appreciated. In advance for any potential respondent, Thank You!
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On 07/21/04 snipped-for-privacy@hotmail.com (Mordido) Writes in part:

1. What Country are you in? 2. What is the brand of the toilet? 3. What are the numbers stamped into the back wall of the tank and on the inside of the tank lid?
Doug
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(Mordido) Writes in part:

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I'm willing to bet this is an Eljer "Touch Flush" model WC which requires a specific size tank ball made for Eljer WC's. Many people make the mistake of putting in a standard tank ball which acts exactly the way being described here, that is, it will not seat properly.
Surely will be appreciated. In

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1) Turn off the water supply to the toilet at the valve coiming our of the wall below and to the left of your toilet. 2) Remove the old flapper, take it to a hardware store and say: "I need a new one of these" 3) Install the new flapper and turn your water supply back on.
Best Wishes
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