Bit more investigation this morning. There are chunks from at least 1 round slider, weight adds up to more than 43g. There is also a clearly identifiable tab from the brass slider. There are some chunks of oily filings welded together, and a few bits of what looks like rubber gasket.
I've decided to do the job properly. So my question now to you more knowledgeable people is if I'm taking the head off, and already got the sump off what is your ideal list of jobs to do while in there? I don't have the space or kit to remove the engine so it needs to be what can be done in situ. Its a 901 prefix S3 2.25L petrol.