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Unfortunately if the oven is off by that much, there isn't much you can do with an old oven like this. The thermostat is going to need to be replaced, there is no adjustment that can be made for anything more than 35 degrees out of range. The thermostat part number you need is 00486945 but it hasn't been made in years so unless you keep searching on Ebay and waiting for one to pop up, it may be time for a new wall oven. I understand that this isn't what you wanted to hear but when manufactures stop making parts it's hard to get around it.
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