There is a user in birdforum: http://www.birdforum.net/member.php?u=71763
If I recall correctly, she used to not like the oly 75-300 lens and liked the pana 100-300 better. Maybe because she had a poor copy of the oly lens? In any case, your problems might be related to something similar? To read more, make a search for posts from her in the oly section or here in the m43 section.