There's a simple fix for this. I drilled down through the bottoms of the posts then put bolts down through the holes long enough to go through the rubbers. Put a little silicone around the bolt heads to keep them from turning. Use a washer and wingnut on the bottom of each bolt. Drill holes in the "wings" on the wingnuts and stretch a spring between them once you get them snugged down. Not only will the play be gone, but there is NO WAY the seat will ever come off. The only drawback is it takes an extra 30 seconds to take the seat off.
__________________
'85 ATC250R
.030 Over Wiseco
FMF Pipe/Answer silencer
36PJ Keihin
K&N
Boyesen reeds
Magura hydraulic clutch
Roost Boost
MSR bars
OMF swingarm skid
ITP Beadlocks
Three Wheelin' Since '84