The Post’s Broadway critic has been revisiting Broadway favorites to see how they hold up over time.

VINTNERS do not approve of putting new wine in old bottles, but on Broadway, it’s done all the time.

Any hit show that has run a year or so – while it may still be making that run on its old reputation and old cast – will almost certainly not have the players it started with.

And even the mechanisms of the productions can – far less frequently than was once the case – grow a bit rusty with the years. So, as has become our practice, here are a few catch-up re-visits.

David Auburn’s Pulitzer Prize-winning and Tony Award Best Play hit, “Proof” (), now in its second successful year at the Walter Kerr Theater, is one of those well-crafted but conventional plays that need to be handled with care.

When this play was first given, it boasted a wonderful quartet of players, led by a truly luminous Mary-Louise Parker, who found a career-defining role as Auburn’s heroine, Catherine, the vibrant daughter of a dead mathematical genius.

Parker has been replaced by Jennifer Jason Leigh, an actor equally sensitive and equally aware of nuance and atmosphere, and equally skilled at the give and take of ensemble.

Compared with her predecessor, Leigh is sexier, edgier and far more convincing as either a mathematical genius or a potential nut case, the two possibilities the playwright poses.

On the other hand, she misses something of the sheer energy Parker brought to the role, and she does not fit in quite so cohesively with the other three members of the cast.

An attractively rugged Patrick Tovatt is now Catherine’s dead father, a man who transformed 20th-century mathematics, then burned out and went quietly mad before his early death. Tovat is convincing as a gruffly loving father, but rarely suggests any hint of a lurking mad scientist.

These are minor quibbles in a production that – largely through Leigh – remains enormously entertaining.

Generally speaking, the upkeep of musicals is even harder than the maintenance of plays.

* It is more than four years ago that “The Lion King” () opened at the grandly refurbished New Amsterdam Theater and instantly became the hottest ticket in town. And now, four years later, with the sole exception of “The Producers,” it still is. Fantastic.

I had heard unkind Broadway rumors that this “Lion King” was getting a little mangy. I didn’t really find this the case.

The difficulty with re-reviewing, or simply revisiting, “The Lion King” is that, unlike “Hamlet” or “Hello Dolly!,” it is not the kind of show you need to see twice. It charms by its novelty – and what do you call novelty the second time around?

Julie Taymor’s marvelously eclectic staging still reveals enormous skill and brilliant craft, as does the truly inventive choreography by the splendid Garth Fagan, and, even if familiar, you still gasp at Richard Hudson’s settings and Donald Holder’s lighting.

The key to everything remains Taymor’s sophisticated yet simple use of puppets.

But “The Lion King” is a musical – and I haven’t even mentioned the music. The main part of the score – as in the original Disney feature – is by Elton John and Tim Rice.

Taymor has tried to change the musical balance of the show with added music by Michael Mancina and a South African chorus – with Lebo M as choral director and vocal arranger – that becomes virtually a character in the show rather than the background score it was in the movie.

All the same, despite the presence of such well-known, if tawdry, songs as “Circle of Life” and “Can You Feel the Love Tonight,” it is the visual effect of the spectacle that counts.

OK, in many ways this is the pure magic of the theatre. But wouldn’t it have been nice if this musical had had better music.

The only survivors from the original cast in their original role are the doughty Samuel E. Wright as the old Lion Mufasa, and the brilliantly funny Tom Alan Robbins as the evil-smelling Pumbaa.

The villain Scar is now played with great, curled-lip disdain by Derek Smith – the best Scar I’ve seen.

* Finally, a brief word on another, more recent musical, Mark Bramble’s stunningly sumptuous revival of “42nd Street” (1/2), at the Ford Center – appropriately, on 42nd Street.

Aptly described to me by a friend as “the quintessential Broadway musical experience,” this is in great shape.

The one big change is the substitution of Meredith Patterson for Kate Levering as a chorus hoofer who becomes an overnight star, and Patterson sings and dances with just the right ingenuous enthusiam and tentative brilliance.