Astra running rough (longish) - Al can\'t fixit
Can anyone make sense of this jumble of (possibly un-related) symptoms?

1999 Astra 1.6 SOHC (Single point injection 8v, 75BHP zzzzz!)
All was going well, despite the timing belt coming off 800 miles after being changed at 80k miles due to tensioner failure. (Repaired at no charge, apparently a non interference engine, & was running sweet afterwards).

Now done 83k ish & running rough. First symptom was increased rattling/tapping noise, worse when engine fully warmed up (or car had been driven for a bit) at first thought to be the tappets but in fact is certainly coming from the injector. (The injector itself has been replaced but this made no difference).
Then started running rough when fully warmed up/driven for about 1/2 hr.
ECU warning light started coming on sporadically, again when warm/driven >1/2hr, turned out to be EGR valve. Replaced. ECU light stopped coming on, but still tappy injector & rough running, now getting more noticable even from cold.
'Chuffing' noise noticable when listening to engine running with oil filler cap removed, allegedly sign of block crankcase breather, possibly due to over-oiling, but oil level certainly ok now & I can't find any crankcase hoses to check for blockages etc.

Rough running seems to be getting worse, but:

Not majorly down on pulling power/compression (just a bit unenthusiastic),
Spark Plugs replaced at 80k service
Fuel & air filters replaced at 80k
No noticable increase in fuel consumption
No noticable oil or water consumption

The above rules out various obvious things, I think.
Any help welcomed.

Thanks,
Al.