Hi Wayne
Rather than half your dose why dont you try spacing out you timing first.Instead of six hourly make it eight and see how that goes.when you start to reduce the actual dose,do it 1 ml at a time halving it is really a bit drastic when you have been on it for so long,and it needs to be very gradual over a couple of weeks.

Withdrawal from long term drug use is never easy and needs to be managed carefully,you will have problems but take it at your own pace.

good luck love liz