No, by adding that much oil, you’ll almost certainly be overfilling the engine which is no good for it at all. It’s a fair bet that an engine that needed an extra seven litres of oil added has already blown up. Which means you can ignore the numbers; they’re probably a part number or batch number.

What you’re looking for are two holes at the very end of the dipstick. The oil level should be between those holes. For whatever reason, Mitsubishi used holes in the dipstick rather than a high and low mark stamped into it. But it works just the same. Keep the oil level between those holes and you’ll be fine.

A leaking rocker cover gasket won’t cause the engine to stop unless it somehow manages to allow too much lubricating oil to escape the engine (which, it potentially could over time). But it still needs to be fixed, because technically the car is unroadworthy with an oil leak and various bits of the car will be getting coated with the oil as it leaks out. Rubber suspension bushes, in particular, are intolerant of contact with oil and will degrade as a result. You might also find the leak is dumping oil on your tyres or the ground in front of them. So it needs to be fixed sooner rather than later.

As for the original diagnosis of your car needing a new engine, I’d be giving that workshop a wide berth as the mechanic in question might be either incompetent or attempting to rip you off. Or both. Your decision to seek a second opinion was a good one and should be standard practice.

I presume you’re not overloading the ute, so fit some Light Truck tyres. Passenger car tyres would be quieter, and the ride would be more comfortable, but you really need tyres capable of carrying the load.