Autofinance guarantee from UG zur GmbH

Hello! The following problem I am self-employed and run an UG. I have contacted a BMW branch office and made a financing request for a car. I was informed that this would not be possible without a guarantee. However, I need a car very quickly and would also like to finance one. I intend to convert the company into a GmbH if everything is going well but that will take about 4 months. I talked to my girlfriend and she has been there for r decided to enter into the guarantee. Now to my question. Is it easier to finance a car with a GmbH without guarantors? If this should be the case, can one terminate the guarantee after founding a GmbH?