amateur vacuum leak hunting

I need some advice / pointers, please.

I am in the process of tracing an erratic idle on a 102 engine (I read that this is referred to as 'stumbling'). Anyway, from the archives I learnt that a vacuum leak can be one of the culprits.

Before I throw money at replacement parts, I want to narrow down the possible sources of a vacuum leak.

How would a vacuum leak be traced?
- listening is out of the question I assume
- spraying a liquid (water) on any possible hose / gasket should temporarily seal the leak but what happens if the liquid is sucked in to whatever causes the vacuum ? Maybe selectively spraying something like carb cleaner or penetrating oil will minimise any damage ?

I have replaced the rotor and the distributor cap and my fuel consumption dropped remarkably, but the 'stumble' is still very evident. It's most noticable at idle. I can feel the car 'shake' at each 'miss' (not violently - just a mild shake of the engine) and the burble at the exhaust is interrupted as the plug misses.

If there is no vacuum leak, the plug leads and plugs are next.
I'll also try some injector cleaner with the next tank of gas.

any ideas will definitely be appreciated.
Regards