Under EU law, no machine or equipment manufacturer can force the customer to use parts or lubricants of a certain brand. By force, we mean the cancellation of the warranty or other consequences for the use of other brands of products. In any book of your car, you will not see the manufacturer say that "Use Polytron 5W-30 oil." EU law makes it very clear that if a manufacturer recommends a certain brand of products (even the original ones) for car maintenance, he must offer them to the customer for FREE.
Unfortunately, many car dealers tell customers that if they do not use their own oil or brand X oil, they risk losing their car warranty. This is an illegality on the face and if it happens to you, tell that car advisor to give you this in writing and you will see how things change.
BUT… brand of oil or parts is not the same as the SPECIFICATION of the oil or part. The dealer can void your car's warranty if you use oil that does not meet the specifications required for your car. Specifications mean (BMW LL01, VW505.01 etc)
Some car manufacturers have sold that 10 cm2 space on the oil cap to an oil company to put their name on it. BMW did this with Castrol. This does not mean that BMW recommends Castrol or that if you do not use the Castrol brand at BMW, the engine will break down. I could sell that advertising space to Pampers too… you didn't put Pampers in your car, did you? You will not see anywhere on any BMW car, books or documentation, write that "BMW recommends using Castrol."
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