Damage to engine when driving w/ high leak down percentage?

[MacFhearguis]

So after running a compression test that came back with low numbers, I did a leak down test, with two separate systems, and got the following results:
1-20%
2-65%
3-12%
4-40%

Now, I know these are bad numbers. The van still drives just fine, and does not have a noticeable lack of power(to me), and no weird hiccups or smoking.

Is it safe to drive the van on a daily basis with these kind of numbers, or is there a risk of damaging the internals of the engine further? This is on a 1985 Westy, with all stock components.

I am also curious as to why the van would drive as well as it does, with these kind of results from the leak down test? Can anyone shed some light on this?

Thanks,
G