Worth a quick check is to ensure that it is not transmission oil in your coolant. This can occur if you have a defective heat exchanger in your radiator. Check the trans fluid on the dipstick - if it is clear then it is probably head gasket. If it is at all cloudy (emulsified oil) then you have a defective radiator which requires urgent attention to save the transmission.
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86 300TE (M103 eng) 230K+ miles (donor car)
95 Toyota Lucida diesel 4wd
86 200T 165K miles (sold)