So this started a few weeks ago when my Fabia started leaking cooling. After a lot of searching around, I found it coming from the bulkhead where the heater matrix connects. There are two alloy pipes that go into the matrix, with a braket attached at the top. Except in my case, the bracket was no longer attaced (what 200k miles does to aluminium). Initially I thought that heater matrix would have cracked too (not just damaged O-rings) , so I was preparing to swap that.
I started looking for a new matrix, and while doing so came accross a PTC heater for £30. An eBay offer later and I had an original Skoda PTC for £15, including clips and bottom housing! See eBay pictures below.
I did confirm it was an option, and the part codes were right for my car before purchasing, but that was as far as I got. As I understand this is the earlier version, that has been superceeded twice to get to the version that fits in the Polo 6R. The following link is an excellent page that shows the newer style, and has some good wiring diagrams, albiet wrong for a Fabia. https://polo.blue/2018/09/02/ptc-retrofit/
Another eBay best offer later, this time of £20, resulting in a 120 amp alternator (thanks @varooom and @Breezy_Pete for the info). Hopefully this is a direct fit. My car has a 90 amp alternator as standard, I will try with that first and log the load factor with VCDS to see if it's viable to not upgrade. You can also get a 110 amp version for a similar price.
Now for the bits from the dealer, this is the expensive bit. I'm going for 100% OEM, so you could omit these and go for generic parts if you want.
6Q0937617B Fuse holder, will add price later but around £10
N01713120 40 amp fuses to go in said holder, you need 3 - Around £1.50 each
1J0972753 - Plug to connect to the PTC heater - Around £10
4B0937527A - Relay plate. You need two. These are around £14 from a dealer which I refuse to pay, so I'll be getting used. It can be any part number, justs needs to fit in the relay frame and support large pin (will confirm dimension) relays.
As for the pins, I'll be ordering them from TE connectivity so I can crimp them to my own wire, and avoid having to splice to repair wire. The OEM relays are number 644 and 645. I will instead be using 70 amp rated Panasonic items as they are far cheaper, and new.
Will update once everything arrives, and once I have details on the pins finalised.