Looking for advice injector seals and o rings

Seen some horror stories on here recently about injector seal and o ring failure.Sometimes sudden.
Some post difficulty in starting as a symptom,obviously increasing sump oil level is another,but are there any other clues to look out for?
My TD5 starts and runs great at mo,but as I am running bio ,weak o rings concern me.
Anyone know if a Viton alternative is an option for the o rings?Or the o ring size such that I can try and source some?
Is there a service interval recommendation for the seals and o rings?
As always grateful for any input ,cheers guys and guyessess

i did mine twice, don't know what we did first time to fail but it did, they were changed as i have an low spot on start up for about 10secs, think it is in tank pump, so have that to do yet, was told to do genuine parts so i did, car done 100k, but when is there a time to do them? i don't know, all ok now with mine, good luck!