I doubt very much temp. has anything to do with it. Although corrosion is a faint possibility, I think it unlikely. The way you describe it, it has not moved at all, is this correct? If so, I am convinced there is still a bolt/stud that needs to be undone somewhere. If, on the other hand, it is moving but only a small bit at a time, corrosion could be the cause, keep working at it. Thank god for oil leaks, they tend to keep everything lubed up enough to separate easily;-) Looking at the rear of the engine, I think there is one at 12 o'clock, 2 o'clock, 4 o'clock and maybe another at 3 or 5 o'clock. Moving counter clockwise from 12 o'clock, there are the 2 starter motor bolts that go through the bell & engine flange and then at 6 and 7, there are 2 brace bolts. That is all I remember.
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Bob Kraushaar '94 945T, '91 940T(back from retirement), '88 240, '84 242T, '94 F-150, '89 560 SL, '68 Shelby GT-500 KR