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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Completely wrong. The grease is decomposed rubber and the part needs to be replaced. Also where it seats needs to be cleaned thoroughly with plastic scrubber or replaced too.
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I agree. These parts are real cheap and just decompose after awhile. That black stuff that comes off is real yucky! I keep at least one spare in the house and just replace it if I suspect a leakage problem. Never had to do anything to the tank seat, but no harm in keeping it clean.
Howard
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What Art said. Replace the 'bulb' flapper. Bring the old one to the hardware store so you can match it up with the same style. They are cheap. The 'grease' is the decomposed flapper. Clean the outlet where the flapper seats thoroughly, if its nicked, rusted or in any way would cause the new flapper to not sit flat then replace that too. Don't call a plumber. It should be a $5, 5 minute repair at most.
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I think you qualify for a scholarship to Toiletology 101 http://www.toiletology.com/index.shtml
Ignore the part where they say it's free.

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This black gook is decomposing rubber. It's caused by the chemicals the water company puts in the water to "protect" us. There are newer rubber compounds that are supposed to be resistant to this chemical. Replace the parts and clean the seat in the flush valve.
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Get a cheap one they dont last.
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