Debian patches are maintained in Git: see Vcs-Git in debian/control.
--- dbus-sharp-0.8.1.orig/dbus-sharp-2.0.pc.in
+++ dbus-sharp-0.8.1/dbus-sharp-2.0.pc.in
@@ -8,4 +8,4 @@ Name: Managed DBus
 Description: Managed D-Bus IPC protocol library and CLR binding
 Version: @VERSION@
 URL: http://mono.github.com/dbus-sharp/
-Libs: -r:${libdir}/mono/@PACKAGE@-@API_VERSION@/dbus-sharp.dll
+Libs: -r:${libdir}/cli/@PACKAGE@-@API_VERSION@/dbus-sharp.dll
