Engine... Overhaul? / Replace? advice please

The engine in our 1972 C172 (0-320-E2D) is now due for overhaul after 2800
hours as lead particles have started appearing in the oil filter. (Top
overhaul was at 1500, bottom end untouched). Still running beautifully, no
vibration, plenty of power, good compressions etc.

We are not sure how best to proceed.

Prices shown are in UK pounds and include taxes (vat @ 17.5%)
In addition to the overhaul we need to add another £1300 to have the engine
taken out and put back in again, (includes the engine mount kit and oil).

One option is to have our existing engine overhauled by a local company
(Jade Air / Norvic) who have a pretty good reputation (they did the top
overhaul about 10 years ago). The cost of this will be about £9987

Second option is to use Norvic but go for their "Millenium" rebuild at
£11491 in which "new cylinders are the
Millenium investment cast type and the crankshaft and connecting rods are
rebalanced to a finer tolerance than standard Lycoming limits" whatever that
really means.

Third option is Lycoming factory exchange "overhauled" £11714

Fourth option is Lycoming factory exchange "re-built" £13914

I understand that with "re-built" you get a new log book. This sounds good
but in practice it is because the engine has been re-built from a collection
of untraceable parts, hence the new log book, so the advantage seems
emotional rather than mechanical!

One big question......
As far as we know, there is nothing fundamentally wrong with our engine and
it has a "known" history, no prop strikes or anything nasty. What is the
chance of finding a cracked crankshaft or something equally nasty?
If we have our own engine overhauled (zero timed) is that better than
swapping it for a Lycoming overhauled engine whose history we have no
knowledge of?

I have heard that engines can only be re-worked about three times before
they are out of spec. If we get a Lycoming exchange engine how do we know
that it hasn't already been re-worked two or three times and would be
rejected at the next overhaul?

It is a serious amount of money to find and I just don't have the knowledge
and experience to know what is the best route to take. Instinctively I
rather like the idea of having my own engine overhauled and keeping the
original plane intact, but maybe I am too sentimental!

Over to you for advice please...

Many Thanks

Les