Advice about Side block oil cooler and O-rings

[MK1_LOVE]

Can I have some advice please?... RE side block oil cooler and O-Rings.

I have had the car looked at for oil leak and garage have quoted for changing the side block oil cooler and the corresponding gaskets.

Having looked at this on the group I have noticed the failure points seems to be the 2 x O-Rings (079103121AD) rather then the side block oil cooler itself
(079117015A/079117015P).

Would there be a way of knowing if the cooler needs replacing or is it pot luck?

The genuine dealer side block oil cooler was charged at £350+ vat alone on the quote, I would only want to replace it if its actually faulty.

Other thing to note is I have seen OE ones listed at a fraction of the price so it makes me think would an OE be part be okay?

Any advice would be great.

Thanks