timing of *.service start-up

Using systemd-185 (kmod 8, kernel 3.3.7) I'm noticing that a 
few of my services are failing (sometimes, not perfectly 
predictably) at boot time. When the failures occur, a manual 
invocation of "systemctl restart <whatever>" always works fine 
to get the services going. So it seems there are some 
timing/race problems and I'd much appreciate any help with 
diagnosing them.

Take thinkfan for example. My unit
/etc/systemd/system/thinkfan.service looks like this:

[Unit]
Description=Thinkfan fan controller

[Service]
ExecStart=/usr/sbin/thinkfan -q -n -z

[Install]
WantedBy=multi-user.target

Sometimes thinkfan starts fine, but other times I'm seeing 
this sort of thing (extracted via journalctl):

systemd[1]: systemd 185 running in system mode.
udevd[60]: starting version 185
thinkfan[153]: thinkfan 0.7.3 starting...
thinkfan[153]: /sys/class/hwmon/hwmon2/device/pwm1_enable: \
  No such file or directory
systemd[1]: thinkfan.service: main process exited, \
  code=exited, status=254