Case back gasket for modern Conquest

Looking for help with a size or part number for the case back gasket.

Newly acquired modern 41mm Conquest Quartz, model L3.759.4.96.6

I’ve looked at a few of the usual watch parts websites but not found anything specific, suspect Longines have control of supply of parts. I just want to locate a new gasket ready for a battery change.

Worst case I can measure the existing gasket , and add a smidge to account for any compression.

Thanks in advance