No worries Lobe,
Penrite, Nulon, Gulf Western all definitely buy their base oils out of Singapore and 100% of their additives from Lubrizoil (confirmed with conversations with their reps and technical people.) As they're 3rd party / boutique oil blenders they don't own any refineries or have the industrial might to produce the base ingredients. This is in contrast to Shell, Mobil, Castrol/BP, Total, Phillips-66, etc... who not only have oil pumping and refinery assets, but are large enough to invest in technical research with vehicle OEM's and produce their own additives (while still in some cases going to Lubrizoil for more generic components.)
Where the 3rd part / boutique blenders attempt to differentiate themselves is at the top of the market with exotic base oils (Esters, PAO's AN's...) which are still bought on the open market, but can be sold at a higher price to a more specialty market where consumers may desire such base oils (note I specifically did not say 'NEED.') They can also release blends for small bespoke markets that the big OEM's have largely abandon (laylend mini with it's common sump for gearbox and engine, that requires a specific oil or air cooled Porsche for example.) Large OEM's aren't going to recoup the investment as the market is so small, but a small blender with lower overheads can turn a tidy profit, with higher profit margins on these specialty products. It's also why you don't see boutique blenders often straying beyond their own domestic market.
For small industry, Penrite also make their products far more accessible (hydraulic, farming, greases...) the large OEM's just want a big $$ purchase order, where Penrite will deal with smaller volumes. Basically when shell can sell aviation lubricant's to Qantas on a long term service arrangement, they're not too concerned with old mate on the farm. Penrite can't match the scale of Shell, so they go for the small scale users who still need to run their machines, but don't have large enough demands to trouble Shell or Mobil.
The consumer automotive space is different, but you'll have noticed that Shell, Mobil and Clatex/Havoline oils have been increasingly absent from store shelves in Australia. Once again, these guys make their cash in lubricant's selling to mining, construction/earthmoving, OEM's, dealerships and Aviation thus can afford to softly abandon the retail space. Thus you see Penrite and Nulon taking up most of the retail and advertising engine lubricant space. Castrol is an odd case here as they continue to push hard in retail, but the point stands.
I'm a mining engineer who deals with mine site ventilation and diesel pollutants, thus have been required to keep up to speed on low saps engine oils for use in underground mining equipment.
regards
Jordan