I have 930D2 diesel unit. One day noticed grass discharge suddenly less, barely any coming out even tho was in tall grass. Figured my PTO clutch was slipping, so I turned off PTO, went to shop. Never thought to look back to see if clutch smoking, so can not say if it was or not. However when I got to shop, engaged PTO again, and it caused engine to die. Repeated twice, same deal. Turned out to be bad 'E' relay. 'E' relay is operated by PTO switch and it operates another relay to engage PTO clutch. Point here is that at first, my unit just had weak clutch engagement, causing slippage and abnormally low grass discharge. If your have same type relay, might be a weak relay causing your clutch to slip.