I sold my 84 diesel, but still have enough 15W40 Rotella T left for one more oil change, and I want to use it for the next oil change on my 89 300SE, which had been getting dino oils every 4k miles. However, I have been adding a quart of oil between oil changes, so I am wondering if it is ok to add different brand different viscosity oils?

Let me "mix" in another question, is there a shelf life for motor oils?

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RH

16 GLC300
12 C250
98 E300D
89 300SE
84 300SD sold