Hello Alex,
My experience in the UK is on petrol and diesel injectors, and the indirect petrol types (injector sits in the inlet manifold nearest to the cylinder head but not actually in the head) are pretty cheap plastic type units and very easy to change.
Direct injection types are straight into the cylinder head, so more strip-down to get to them, and the injectors are very heavy duty steel items to handle the very high pressures / temperatures and cost 4 or 5 times more here (for refurb that is!)
In terms of risk, what do you see, any leaking fuel in / on / around the injectors or cylinder head?
If so, this is the most dangerous and should be remedied urgently.
If you don't see any fuel but only smell it strongly, then yes it may just be leaking badly into the manifolding or cylinder (depending on indirect or direct type) which poses much less external risk, but will mean that cylinder is running excessively rich / wet so;
i)Petrol will soak the plug and may misfire or make starting more difficult.
ii)Will suffer bore wear in that cylinder as the excess petrol washes off the oil film that deliberately protects / lubricates the cylinder wall. Longer term running in this state may accelerate wear and lead to loss of compression and smoking from that cylinder.
iii)Increased emissions levels
iv)Could suffer mechanical damage to the piston / connecting rod if too much fuel leaks into the cylinder, although this would require the pumps to be working and the injector to be virtually running like an open tap.
A lot of places refurb injectors at a cost way lower than buying new, and this is absolutely fine to do, so check that out as well, but in any case bad fuel leaks, inside or outside of your engine are not good and will cause damage one way or another so it really is best (and cheaper) to get them fixed as soon as possible.
