Usual cause of death of alternators are the brushes wear out. I think Leons' are Bosch & Valeo.
If bosch, this is the one I fitted last month. £23 ish, It was genuine Bosch & fitted & worked perfectly.
https://www.ebay.co.uk/itm/Alternat...6-3-2-99-to-04-Genuine-Bosch-New/233851253426
Better still, they can be swapped in situ, without dropping the alternator (a pain on my TDI)
Bosch part numbers are a complete pain. There are hundreds for what often seem to be the same part.
I think that each time they supply a car maker, they put a different part number on it.
So making it harder to cross reference, also they can charge more for the "correct" part.
By the way, my Leon brake master cylinder is the same as for a Ferrari Testarossa.
Bet you, a part supplier's prices will not respect this fact.