also . date stamping on boot lock..

It will be older than a 1993 as Minis were all 1275 cc after that date.
Check the boot latch it should have a 4 digit code on it ie: 14 88 which would represent the 14th week of 1988 as the approximate build date, the wiper motor also has the 4 digit stamping.
Mayfair is a trim level not the make.

I have a Mini of very similar age that was an export to Germany. It was also classed as a Mayfair. As far as I know, that designation merely refers to the level of interior trim etc. For example, mine has the 3-clock instrument pod in front of the driver (which includes the tachometer), cloth interior, leather-wrapped steering wheel and rear side windows that open. Mine does not have the woodgrain dash panel - only the more traditional open parcel shelf. Mine also has the side marker lights. Cheaper versions had a 2-clock pod and fixed rear side windows.

I suspect your woodgrain dash and "Cooper"-branded steering wheel may be after-market add-ons.

You should be able to find the true chassis number by looking in the cowl gutter at the back right corner of the engine bay. Open the bonnet and look in the gutter above the windshield wiper motor. You may have to remove part of the rubber weatherstrip to see it. The chassis number was stamped into the metal during fabrication. It may be obscured by paint if the car has been repainted - mine is readable even though the car has been repainted at least twice. You might also be able to read it in a mirror placed under gutter.

In Austria, a vehicle collection was abandoned, including several minis auctioned where unfortunately the vehicle registration were lost. Can someone help me with the research? - The chassis number is SAXXL2S1S21489599. As far as I know, the chassis number would have to be composed as follows:

SAX for MG-Rover
X without meaning
L for the 998cc
2S for the 2-door
1 classic round nose mini body
S Mayfair class > special model?
2 for the model year from 1984?
1 LHD left-hand drive

….so far so good. - However, I have a steering wheel in the vehicle of a COOPER, but since 1984 actually no Cooper execution was built? However, the dashboard is done in root wood grain, which was previously done before in a Cooper. Furthermore, the vehicle already has a side indicator, so you can narrow down to a BJ from 1986.

Can someone tell me more about this vehicle? - We try to define an exact year or better and want to understand why this vehicle was titled Mayfair.
Thanks for your support!