Originally Posted by brawls43
If you can see what color yours has, add the same type, green or possibly yellow. Do not use the orange DexCool for GMs.
Sidenote: The proper size O-ring to use is actually a METRIC o-ring. Remember that Ford converted all its cars to Metric, not to mention the Focus was originally designed in Europe, where metric is the standard. After reading some people used #203 and some used #202, I checked into the metric's and there happens to be a standard metric size right between a #202 and #203. Its a 7mm ID, 13mm OD, 3mm cross-section. I got mine in Viton and of course have some left over. It went back in easily and haven't had a leak since. If you need one, PM me and I'll drop one in the snail mail for you.
Sorry, I'm now out of the o-rings I bought, they can be ordered from places like McMasterCarr.
I just did this, and ordered the metric oring from mcmastercarr. I looked around at all the local automotive parts shops, even a few 'specialty' shops that I was told might have metric o-rings, with no luck.
After getting the o-rings, I switched mine out in about 10 minutes. The metric o-ring fits really well without having to force it. about 1/2 gallon of coolant comes out, but it's a fairly quick switch.