Try mounting sources as none if all else fails.
 [rsc] --rwxrwxr-x M 1250499 glenda sys 1027 Jan 25 20:47 rc/bin/9fs
	/n/sourcesdump/2006/0125/plan9/rc/bin/9fs:20,26 - 
	/n/sourcesdump/2006/0126/plan9/rc/bin/9fs:20,28
	  case juke
	  	srv -q il!jukefs && mount /srv/il!jukefs /n/njuke && bind -c /n/njuke/juke /n/juke
	  case sources
	- 	srv -m tcp!sources.cs.bell-labs.com sources /n/sources
	+ 	srv -q tcp!sources.cs.bell-labs.com sources /n/sources &&
	+ 		{ mount /srv/sources /n/sources ||
	+ 		  mount -n /srv/sources /n/sources }
	  case sourcesdump
	  	9fs sources
	  	mount /srv/sources /n/sourcesdump main/archive