How much vertical play should there be in the castor fork spindles? Mine seems to have more than expected, perhaps as much as a sixteenth of an inch. On uneven ground, when the weight comes off one of the castors, I can hear an audible "clank" as the fork drops. Is this normal? Could the bearings possibly be installed improperly? Also, there are no grease fittings and the owners' manual has no instructions on adjusting, cleaning, lubricating or repacking these spindle bearings. Is there any periodic maintenance required, especially when the mower is used in sandy soils such as we have here in Florida?