The turbo sounded fishy, so I looked for a replacement. On eBay I found a seller offering new turbo’s for a Mitsubishi L300.
Brantho-Korrux 3 in 1 is described as rust preventative paint, primer and top coating, all in one. Because it’s available in just about any RAL colour, it could save some time.
I’ve used POR-15 for years to prevent or stop rust. The coating is a bit flexible and doesn’t get damaged easily.