I recently installed an acdelco pf48. The base plate nut did not look flat with the base plate. The filter doesn't leak so I assume the nut self-aligned when I tightened the filter.
I presume others would have returned or exchanged a filter that looked like this one, but it worked out OK this time.
I presume others would have returned or exchanged a filter that looked like this one, but it worked out OK this time.