As always, it depends.
If the rest of your engine seals well, then the PCV valve probably doesn't
matter much, except possibly as a flame trap.
If the rest of your engine doesn't seal well (like, through the oil filler,
around the valve cover, the dipstick...), then you may have a huge vacuum leak,
though that pipe and the engine. You should notice a difference in the idle as
you pull the oil filler cap off and allow outside air into the carbs. If you
don't, you have a leak.
There are lots of generic PCV valves on the market; the trick is finding one
that plumbs in well. I fiddled with a lot of different attempts on my TR4A -
the problem there is that the routing is very tight, and the stock unit takes
the same size hose on both inlet and outlet. None of the currently manufactured
valves do that - they are sized differently to make it obvious how to install
them. I finally gave up and went back to stock parts, mostly because I couldn't
get rid of all the vacuum leaks, and because my engine currently has enough
blowby that the PCV valve I was using didn't handle it and would clog, causing
me to lose oil out the valve cover.
On my GT6+, I am very happy with my aftermarket PCV valve and cobbled fittings.
It took a while to get them right, too, and the engine is in better shape.
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