I may try the additive then and see what happens. I have a 40mile commute to work mainly A roads and motorway. The only time it's sat in traffic is on the way home for around 10 to 15 mins, but that's still moving just slowly.

Would the stem seals not cause it to smoke on start up or after long periods of idling?
I carried out an oil change 8 weeks ago and it has dropped from halfway on the dip stick to just above the minimum.

Just out of interest, what oil did you use?

I used Selenia Abarth branded 10w50. From what I could see that was the right one for the car

So a little update, I have driven around 250 - 300 miles with Forte seal conditioner in and it has not made any difference. I have also been carrying out a few other tests.

These are,
Cold start after the car being sat for 5 days. No smoke on start up
Long period of idle ~ 20 min from cold, then driven off. No smoke
Long period of idle ~ 20 min after 1hr drive then drive off. No smoke
Engine brake down long hill in 3rd, 4th, 5th gears drive after. Large plume of bluey white smoke that lingers and smells of burnt oil
Coast down same hill with clutch in then drive after. No smoke

Does this still sound like turbo oil seal?

Now Im not so sure its stem seals. I need to ask, has this only occurred since oil and filter change?
Reason I ask is because if you drained oil sump but refitted sump plug before changing oil filter, then theres a possibility that the remaining oil in filter housing hasnt drained to sump and might lead to overfill, which would then possibly cause excess pressure on oil seals.
Can you tell me part number of replacement oil filter you used and do you remember how many o rings you changed?

Now Im not so sure its stem seals. I need to ask, has this only occurred since oil and filter change?
Reason I ask is because if you drained oil sump but refitted sump plug before changing oil filter, then theres a possibility that the remaining oil in filter housing hasnt drained to sump and might lead to overfill, which would then possibly cause excess pressure on oil seals.
Can you tell me part number of replacement oil filter you used and do you remember how many o rings you changed?

To be honest I never noticed it before the oil / filter change, but then I wasn't really looking for it. Also I can't remember if the drain plug was out when I changed the filter. However I don't think that it is overfill as the oil is around 1/3 up the dip stick.
I have no idea what the part number was sorry and pretty sure it was only 1 o ring that I changed. Is there more??

One other thing, has the dip stick been changed?

I know it has not but measure yours and I'll measure mine

Red handle

52cm from base end to flange that stops the stick at the top