What garage did you take it to ?
The engine mgmt light (EML) is a common sight on the Aero dashboard. It can be triggered by a lot of things. If yo uhave not run the car for a while and the fuel is a bit rough then it will qiote possibly trigger the emissions gubbins. A full tank of premium, a heavy right foot so it all heats through well. Switch off and leave it. Do the same again and next time it should go off. Getting the engine warm given the light weight, power and buy roads can cause this. I caution this if you have been told there IS a fault in case it makes it worse. If you are parking up for winter then drop some Sta-bil (Keeps petrol more balanced over winter layup) in it to help with this.
It is quite common to find the Mass Airflow Sensor becomes a bit iffy over time. This is known for triggering the EML and is common on BMW as well as Morgans with this engine. It is not a big part but it does require some effort to get to and fit as I understand it.
Example- do not buy this one as I am not an engineer and might have guessed the wrong one!
VANOS is the camshaft system. The Plus8 has the BMW 4.8L V8 engine with "double VANOS" meaning that as the revs rise it adjusts the camshaft timing. It uses oil pressure and a computer to adjust the opening and duration of the inlet and exhaust camshafts (hence double) to raise the power output. It is why you should get a little more growl as it goes past 4000 rpm under an open throttle. If you are driving and open the throttle to accelerate can you feel it "pick up" the strength of the cceleration as it goes past 3750-4000 rpm which is when the vario stuff should kick in and give you a more aggressive cam profile. Doing it on a small throttle angle will probably not provoke it, it needs to be given some welly. If you are not feeling any change it might be that you have an issue with the variocam engineering which is what underpins the "VANOS" marketing term.
I believe that there is an oil feed collector in the sump that sucks up the oil to drive the pressure that pushes the cambits around. In the past I was told that if you bash the sump (easily done on the low mounted 4.8) it can block the input to the oil collector and then the mechanism can suffer as a result. This means a top end rebuild which as you have been told is not cheap. I am on my third sump and going to fit a Wolf Sump Plate. Get a local garage to put the car up on ramps and have a look at the sump and oil filter for grinding and damage.
Outside of this I would recommend trying a known good Plus 8 from someone near you to see how that feels as the VANOS kicks in to compare ? Then it's off to the Morgan Aero skilled dealer. If you can get the specific codes from the people you went to in advance of speaking to the Morgan dealer it should help.
Depending on your IT comfort level it is good to have an ODB2 device (search for ELM327 as an example) and phone/tablet with some software to read the codes it finds. There are many including Carly, Torque etc. If you live in fear of it then your local garage usually has a little ruggedised tablet provided by Snap-On which is the pro version and can read things as a guide so your chosen Morgan garage has something to start with. It can be a treck to get to one of the dealers so this provides a quick catch-net.
Hope that helps. I am not a car engineer but have lived with Aeros for a bit and seen this often. It is a rugged engine/box/axle but the exposed sump is a weakness of the platform. Sleeping policemen are not your friend.
We have some very skilled people on the forum, I am certain others will be along shortly.
