My friend had FTE issues with his using WWB. We found out later the ammo is underpowered and the recoil spring needed breaking in before we could use the milder stuff. AFAIK the gun runs fine now after a couple thousand downrange.
I've got my own complaints about WWB, being underpowered isn't typically one of them. Dirty yes, inconsistent yes, but it typically has enough umph to get the job done.
I love these "breaking in" requirements. I had to "break in" a new HK P30 as well. IMHO, it's bs.