I have a Shell service station nearby & i read the labels on the oil bottles to pick the one i need for whatever i'm driving. They have one for older cars, which suits my 200B. I overhauled the engine thats in it now as a temporary measure untill i reconditioned the original, but despite the bore wear, it drinks almost no oil & runs fine, so temporary is an elastic measure & it's getting stretched. That oil works for me.

In the GX engine, when it was on the road, i used a higher quality, high detergent oil of 10W/30 & changed it & the filter every 5,000 miles [8,000k] For road use in a touring engine, it kept the engine clean, & i never had any problems in the lubrication dept.

In my fleet of Moto Morini motorcycles [i had 3 of the late '76 shipment batch of 10 all at the same time.] I used Penrite HPR30, & changed it every 1,000k. They had no real oil filter to speak of & the gearbox ran in the same oil. I used a magnetic sump plug as well. What a revelation that thing proved to be.

All the major brand names make good oil, you just gotta pick the one best suited to your engine & driving style.
Chris

P.S. If you are running an A series engine, you will find that there are two filters. There was a long one for 1200's & 1000's, which was replaced by a shorter one for 120Y's & later. They are interchangeable & the earlier one has much more filtering medium, so thats the one i always used. I use them on my son's 120Y for that reason also.

I think that Penrite is a small Australian company & i do not know if they export. Type "Penrite" into a search engine & see what pops up.