is the car breathing heavy ?
does she breath like a boiling kettle from the dipstick ?
that's the biggest sign of worn pistons but doesn't necessarily mean high oil consumption
oil stem seals dont seem to be an issue unless the car has had work done before [head gasket] and they cut corners in not bothering to replace them after taking the valves out, or they simply havent fitted them correctly, I haven't owned a vauxhall yet with valve stem seal problems, people instantly think it is valve steam seal problems when infact it is usually ring wear
my car doesn't burn oil, never seen smoke when revving her but i had low oil level reading and it was going into the bell housing as a result of the man shaft oil seal, cant say how long it has been leaking oil but i lost around 1.7 litres, common places for oil leaks are the cam cover seal, tensioner seal, crankshaft seal, power steering pump seal, i have even seen oil leaks from the water pump
best way of checking oil is get the car level and run her from cold for around 5 minutes then clean dipstick and check 3 or 4 times
most vauxhall's with high mileage burn oil, doesn't necessarily mean the engine is fubar,
if it is bottom end damage and your not a competant mechanic then your better off finding another engine, as the serviceable parts will cost u hundreds then u looking at labour and possible piston replacement & rebores, crank damage
intake systems will get clogged up as a result of heaving breathing
u wont know full cost of replacing rings until u split the engine as u might have cylinder wall damage thus resulting in re bore and possible bigger pistons
u use thinner oil then expect to burn it off, every performance car burns oils so it is common sense the thinner the oil the more your going to lose [fully synthetic ]
the oil jets pass oil through to lubricate the chain to stop it stretching and snapping [friction]
my first car was a nova 1.0 [1996] and i drove her into some deep water and forgot i had a bolt on k&n, the engine seized up but i got away with using diesel to loosen her up, result was fecked bearing and damaged crank, i drove for her 18 months [20000 miles] using 5 litres of oil every 6 or 7 weeks, and i still sold her on starting up first time 🙂
my old calibra x20xev was a heavy breather and in the end lost compression on one cylinder, signs were the rings were fubar but i still got 6000 miles before i end up replacing engine
it is down the owner to repair the problem if no signs of oil leaks or drive it into the ground, i am personally the latter 😛
if i was you the first things i would do is ;
1, jack the car up and get underneath it but use axel stands, looks for leaks around the cam chain cover and crankseal, and anything obvious
2, get a compression tester from halfruads and test the cylinders
then come back to us with the results