I checked my vacum advance last night and found there was no resistance to me sucking or blowing.
The car runs fine and ticks over nicely.
What are the downsides to having a leaking unit?
I am hoping to get another uno for spares and so will transplant this unit soon.
A failed vacuum advance will make the engine run on the weak side, as with no resistance from the vacuum unit the carburetor will draw extra air in from the connecting pipe. More air = weaker mixture.
Normal symtoms for a failed unit are poor tickover, stalling and hesitation when accelerating. Your distributer also won't be giving the correct advance/ retard settings for the ignition.
If you've got access to a timing light, check the timing. If the timing is set correctly (vacuum advance pipe disconnected and plugged), the engine will tick over roughly. Once the pipe is reconnected, the correct advance/ retard settings come into play and the engine will tick over much more smoothly.
It is possible to get the engine to tickover ok with a failed vacuum unit, but the only way to do this is to adjust the distributer until it runs smoothly. This is ok at tickover, but the ignition settings will be out as soon as you rev the engine.
They're not expensive, so for peace of mind fit a new one, or one from your spares car