explaining the use of either vs as well in a negative sentence

[D.C. Foster]

I'm trying to mark the following sentence and I want to explain the correct use of either vs as well in this case. So ignoring the other mistakes in this sentence, how could I best explain the correct usage of either (instead of as well) in this sentence "But it doesn’t mean that it has not disadvantages as well" (the preceding sentences were talking about the advantage of having a car, now they are switching to the disadvantages).

In my mind the correct sentence would be "But that doesn't mean that there aren't any disadvantages" or "But it doesn’t mean that it has not disadvantages either"

But to be honest, I can't seem to come up with a straight answer in my mind so your help would be appreciated!

Thanks

 

[The Maltese Falcon]

The sentence is negative, so it is correct to use either.
In a positive sentence, you would use as well.

There are other disadvantages as well.

 

[Tdol]

But it doesn’t mean that it has not disadvantages either

I'd use has no disadvantages.