how to unstick NFS freebsd 4.11

[Vivek Khera]

Running a box I just upgraded on September 30 to 4.11-STABLE.

I have what appears a wedged NFS client.  The NFS server was recently  
replaced with a new box after a failure.  However, now the client  
can't umount the old one.  How can I clear this up without a reboot  
(which is a *painful* thing to do on a production box):

[root at w02]# ls /n/lorax1
ls: /n/lorax1: Stale NFS file handle
[root at w02]# df
Filesystem    1K-blocks     Used   Avail Capacity  Mounted on
/dev/amrd0s2a    128990    41902   76770    35%    /
/dev/amrd0s2f    201518    38654  146744    21%    /u/w02
/dev/amrd0s2e    604718   396194  160148    71%    /usr
/dev/amrd0s2g  15285872 12972172 1090832    92%    /var
mfs:23            32206      354   29276     1%    /tmp
procfs                4        4       0   100%    /proc
[root at w02]# umount /n/lorax1
umount: unmount of /n/lorax1 failed: Device busy
[root at w02]# mount /n/lorax1
mount: /n/lorax1: Stale NFS file handle

also, fstat shows nothing sitting inside of /n/lorax1 as its working  
directory.