Mayonnaise and the oil separator (in UK weather).
Memory lane section
I worked on Guzzis in the late 80s and 90s [at Ian Smail's in Bristol] and I recall that one of the big advantages of getting rid of the airbox was stopping the mayonnaise build up in the rocker boxes.
We had little or no mayonnaise on older bikes fitted with the small pressed steel oil separator with the non return valve. However when Guzzi introduced the 'new' black plastic oil separator some bikes filled the cylinder heads up with the sludge.
So when owners asked us to remove the airbox we used the old oil separator and never saw the problem again.
We found that clearing a 'clot' of mayo out of the separator box cured the problem at least temporarily so it seems that the flow through the box is easily stopped. I did try to 'improve' one of the black plastic separators by removing moulding swarf and opening the holes fully..... the owner never came back but that could mean....anything.
Conclusion of the ramble...
Could the mayonnaise problem relate to poorly moulded oil separator boxes or kinked breather tubes?
we did not install K&N air strainers - we used foam one piece 'sock's and they were great until rainwater dripped onto them from the seat and stopped the airflow!