I might be the first guinea pig or test mule ........ but Shad plugged the breather on my snout a few weeks ago as the spewing all over the timing belt etc. at the track was just not acceptable. Since then I drove a full track day (about 4 sessions of 20-25 minutes), another track day that didn't count for much, and normal street driving for some total 600 miles. The level has stayed steady at the lower mark - and I suspect part of it is due to the number of times we checked/wiped for the oil level. The oil will expand under heat and constant boost, so you need some room for it to expand - and I suspect everytime we checked it right after a session we wiped some off.
The issue is not whether one track day or session will affect the oil level or the seals. But how long such a set up (i.e., plugged) will cause premature wear of the internal seals as the pressure built up with 13K revs is noticeable - you will hear the hissing sound when you open the cap.
A few weeks ago, I exchanged several e-mails with Lysholm re this same question, the gist of their response is: the plugged solution works in most cases, but every application is unique. Based on the past history of one vendor delivering successful installation with non vented oil cavities one would assume that it works - however, they have no records though on their endurance test activities for this application. No guarantees and no warranties. YMMV.
j/k
