Deductions & credits

Basically my question I just asked with an extra twist of the different cars belonging to different owners.  For sure I never deducted actual costs, they would be a nightmare.  And since I was never offered how to deduct mileage, it looks like I never deducted vehicle expense in some 5yrs.  It's about 20% of profits so quite a bit of money lost.  Like original Q is asking, how do we get the mileage in? I found a place with a kind of a miscellaneous entry but it looks weird with no other vehicle expenses.  Audit red flag?