I've recently purchased an 87 5.0 GT and while driving it around I noticed the stock oil pressure gauge fluctuates from the bare minimum line of normal to about the 2nd and 3rd lines. But once warmed up it stays around the bare minimum line of normal just above the red 0 line. I have read that the sending units are prone to going bad. The car does have what looks like an oil pan leak. Most of the pan is covered in oil. So my question is can an oil pan leak cause low oil pressure? The other question is can I replace the sending unit without draining the oil?