Brian,
Been off the board for a while. If the plugs have the same heat range it really shouldn't make a difference, but that's my sole opinion. They may be right about the oil. Some oil is normal, it's just difficult to guage. There are a couple of devices in the fuel injection system that can make the car run rich when they fail. One is the oxygen sensor(s). The other is the air mass meter or sometimes called the mass airflow sensor. The engine management system defaults to an overly rich mixture when it doesn't get a signal from either of these devices, which keeps the car running, although poorly. Without these defaults the car would quit or risk a lean condition which could result in extreme engine damage, especially on the "R". Usually any problems like this would kick on the check engine light and generate an error code.

Good luck, Mark