May not be the same thing at all, but on my old Mondy V6 I span the shells due to low oil I guess. Sounded like you describe.

Got quotes of £1500 + for 2nd hand bottom ends.

In the end got some shells from a Cougar in the States (same motor) for £70 and my good mate fitted them in the morning - that and and oil change cost me £100 and lasted just fine.

Don't keep running it, it'll only get worse.

Si