Technican b says:
the chisel thing is what i usually do, if that doesn't work get a file and clean the bolt up a bit, spray some wd-40 or pb blaster on it and let it sit, get a 6 point socket and tap it onto the bolt, if it is rounded off file it down to the next metric or standard size and then tack a socket and tap it on with a hammer, (get a shallow socket) when its on get a ratchet and give it a quick pull, if that doesn't work or nothing else will chances are if you take it to a shop they will want to replace the whole pan for liability reasons, if thats the case- go buy a pan for cheap if you can't find one i may have one, and put it on yourself and save some money.
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