To buy, or not to buy, that is the question.

Hi folks, I went back to school earlier this year, but I obviously didn't learn enough. I am helping create the financial statements for some local startups in the area, and I ran across a question that I can't quite figure out how to solve.

One of the startups has actually been around for 5 years. It was acquired by the current owner, and it appears that the current owner has some assets that are quite costly due to repairs. I want to tell them to sell off the asset, and acquire a newer replacement, but I would like to show them the numbers as to why that would make more sense for them. I know that I can use a DCF model to show why acquiring a new model would be ideal, but would that be enough? Is there another model I can create to compare buying vs repairing?

Thanks for your help.