Wowser, almost as much "bling" to that piece as Captain Corelli's mandolin.
Olive oil, the staff of life for Mediterranean people, with a variety of uses besides eating incl a traditional personal lubricant (maybe that's why "extra virgin" is always more expensive)

and a hair and skin conditioner. Its even great to feed to a cat to help with hairballs too.

Tomatoes are in season now and I've been enjoying it in bruschetta and as a topping over chopped tomatoes on humus. I've even had a few olive oil massages and that was pretty nice. And now we learn about a more arcane use to treat the parkerizing on Garands back at the Breda works 60 years ago, and right down to the precise brand name of the olive oil.
The correct color of Parkerizing is always a great discussion point with a lot of inconclusive results. The color of Parkerizing is highly variable depending on several factors incl the type of Parkerizing used (zinc or manganese based), the type of steel being parkerized, the preparation of the steel surface, the strength of the Parkerizing bath, and the treatment of the surface after being removed from the bath. The final color can range from light grey to black depending on all of the foregoing. The standard treatment for newly parkerized steel after a cold water rinse and the application of a petroleum based stopping agent is to coat the metal surface with oil and allow it to cure for several days. Anything from engine oil to 3 in 1 oil (my personal choice) can be used for this. The general consensus a on green tinted parkerized finish is that this results from the effect of the chemicals in a protective coating of cosmolene after a period of storage. This is especially evident on US Army 03-A3 Springfield rifles which were kept in depot level storage for quite a period of time prior to disposal. Tough to say about the original color of a parkerized Breda receiver as so many have been re-parkerized over the years, but my view is that is was kind of a light French grey. I once owned a 2K s/n Breda rifle with what I thought to be the intact original finish and this is what it looked like.
Bruce Canfield's recently published 872 page book on the Garand includes an extract of a 1954 dated letter on page 611 concerning problems that the Italians were having in establishing the correct Parkerizing color for their Garands. The letter is a response from Springfield Armory to a query from the Italians and it indicates that the final finish will range from dark grey to black, provided that the finishing procedures in US Army TM9-1861 were followed. I haven't seen TM9-1861, but I'm thinking that the standard procedures did not include a post-Parkerizing treatment with olive oil of whatever brand. Olive oil has a considerable acid content and that and steel don't work too well, although the parkerized finish would certainly offer some resistance to the corrosive effects of the acids in olive oil. I wouldn't use it on any of my firearms for this reason.
I'd like to know more about the source of this information and it's reliability. No doubt Bruce Canfield would have liked to add it to his book if it could be authenticated. It's been 60 years since Breda/Beretta ran their Garand production line for Denmark and much of the technical details have no doubt been lost in the sands of time as old manufacturing records and processes tend to get discarded over the years. Maybe old Luigi or Antonio down in the receiver finishing room at Breda had a "eureka moment" when they accidentally spilled some olive oil of a specific brand from their lunchbox onto a freshly parkerized Garand receiver

, but who knows. Anyway, I like to think of them harmonizing a duet of "O Solo Mio" as they lovingly caressed those receivers with olive oil.