Hi tesseract. Welcome to the forum. Whether or not the distributor cap is removed is of little consequence. Is there a reason you are concerned? Most mechanics would take the cap off when removing the distributor so they wouldn't have to unplug the spark plug wires. That just saves time and eliminates the possiblility of mixing them up if he gets distracted.
Depending on the symptoms, there are two oil seals in the distributor. One is an o-ring on the outside of the base. If it leaks, oil will run on the outside of the engine. There is also a lip seal around the distributor shaft. Oil won't typically run out of that one, but vaporized oil can sneek past it and condense on the pickup assembly. If your pickup is of the optical type, the oil film can cause the engine to stall or not start. That is somewhat common on older Toyotas. Mitsubishi uses a similar design but has very little trouble.
Even if your car doesn't use an optical pickup assembly, the vaporized oil can condense inside the cap where it will short out the spark plug's firing voltage. That willl result in a misfire that could be intermittent. You didn't say why your distributor needed to be removed, but I can't imagine a mechanic repairing something related to it and not removing the cap to inspect it, the rotor, and the pickup assembly.
Besides the inspection, there is a gear on the end of the distributor shaft. If that gear is off by one tooth when the distributor is reinstalled, the engine won't start. Standard procedure would be to remove the cap and observe where the rotor is pointing, then making sure it is pointing the same way when it is installed again. If the mechanic is careful to not disturb that gear while the distributor is removed, it may be possible to reinstall it without removing the cap. I wouldn't trust myself, but that doesn't mean it can't be done.
Saturday, April 10th, 2010 AT 7:58 PM