SL1 Blowby?

One of the old tricks I learned when looking at used vehicles is to take the oil filler cap off and feel for escaping pressure. This was to see how much blowby or pressure was escaping past worn piston rings. Today I looked at a 1998 SL1 with about 110k miles on the engine. When I pulled the oil cap off, there was substantial pressure coming out the hole at idle. The woman who owned it said it didn't use oil. It ran great otherwise.
Is it normal on the Sl1 to feel so much hot air escaping the oil filler hole when running? I have not noticed this in other vehicles I have looked lately. I usually feel a pulstaing type effect where you can feel it blowing and sucking, indicating simple piston up and down displacement, which I think is normal.