Entering Ukraine with someone else's car

I am planning to travel to Ukraine for a couple of weeks this summer by car, but the car is not registered in my name. I know from experience that other countries often have special regulations for such cases to prevent transport of stolen cars. I do of course have the car registration papers and a green insurance card valid for Ukraine, but do I need any further supporting documents, since it is not my own car?

I have already found a lot of conflicting information on the net or in different fora, so I would really appreciate if any answer would also link to official resources, be it in Ukrainian or English. I have already tried to contact Ukrainian authorities, but I don't get any answers.

• I have not found any information on the Ukrainian Customs' (State Fiscal Service) web pages.
• I have not found any information on the Ukrainian State Border Guard's web pages.
• I have not found any information on the Ukrainian embassy in Germany's (where I live) web pages.

My situation is mentioned in the travel advice for Ukraine from the German Federal Foreign Office. They claim that I need a notarized and apostilled power of attorney from the car's owner, which has to be translated into Ukrainian by an approved interpreter. I am however not sure if this information is up to date and this information is in any case not authorative. The subject has been discussed in different internet fora, where it is both claimed that an informal power of attorney is sufficient (no need for a notarization, apostille or proper translation) or that a power of attorney used to be required, but the requirement has been lifted completely.