"He walks as if he is drunk." Grammatically correct ? Any difference in meaning from "...as if he were drunk."?

'Melanie' explains this usage of 'as if':

As if [can be] a [subordinating] conjunction. It is used to say how something seems from the information known. It is a more formal way of saying like, and is used in the same way as as though.

In ... the following sentences and examples, as if can be replaced with as though and like (in informal conversation).

It was great to see Luke again. It sounds as if he’s doing well in life.

My friend is under a lot of pressure at the moment. She feels as if she has the weight of the world on her shoulders.

These examples use the indicative.

Although English Grammar Forum gives both the indicative and the subjunctive as grammatical options:

It looks as if it’s going to rain.

It feels as if it were going to rain.

the subjunctive sounds rather dated, high-falutin – even faintly ridiculous to my ears. The 'as if' conveys the sense of uncertainty perfectly adequately.

The situation with bare 'if' is not the same, where 'if he were drunk' and 'if he was drunk' usefully disambiguate.

What I have found bears out @John Lawler's comment.

Many grammarians (mostly purists) insist that both "as if" and "as though" must be followed by a subjunctive, not by an indicative verb, since they put an imaginary case (as he would if he were, etc.) But do they? There is surely a distinction between "He walks as if he were drunk." (implying "but he is not") and "He walks as if he is drunk", meaning "He is drunk judging from the way he walks". Similarly we have "It looks as if it is going to rain." (= It is going to rain, by the look of it), "It looks as if we will have to do the work ourselves". For these the indicative seems justifiable. https://openlibrary.org/books/OL14999310M/Current_English_usage.

Therefore, one would probably say "It looks as if it is going to rain" when the weather looks like that, but he could say either "as if he is drunk" or "as if he were drunk", depending on his degree of certainty.