Valve cover gasket.

[datzenmike]

The problem, as I see it, is that today's oil has about half (around 600 PPM or lower) the ZDDP levels that did 20-30 years ago and it seems to be still lowering with no end in sight. Zinc is an anti scuff additive used to protect solid lifter cams or 'flat tappet' cams. Most are roller rocker cams today and the zinc ruins the latest catalytic converters thus it's slow phasing out. I recommend you look up the ZDDP controversy in relation to older engines and make a decision based on knowledge of what's involved here. Diesel oils are exempt from lower levels of ZDDP and there are several including Chevron Dello 400. Additionally oils labeled 'Racing' like, (but not limited to) Valvoline VR1 are also good. You can also add ZDDP additives to your oil but why not just get the right oil to begin with. 

 

I'm using Shell Rotella T4 15w40 although I recently saw it in 10w30 as well. I only drive in the summer so I run 40. I don't believe in synthetic oil in out Datsuns, even if rebuilt. They don't need the extreme protection offered and are just too damned expensive to change merely because it's dirty. Synthetic is made for to-days tighter tolerance engines and I find it seeps past old seals and gaskets. 

 

Protect your L series no one else will...

[Charlie69]

I run the Shell Rotella 15/40.  $13 a gallon at Walmart.

[difrangia]

I use a ZDDP addative (I think Rislone brand, I'd have to look) on new rebuild of old engines and use Rotella-T from the start. My dad was a Chevy dealer mechanic through the 1950's and he swore by GM's EOS (Engine Oil Suplement, ZDDP concentrated additive) for use at rebuild.

[bottomwatcher]

Yes! For some crazy reason diesel oil seems to be on sale for half the price of regular oil. I use it in everything from the 720, mowers, pressure washers the 68 beetle and of course the Duramax and diesel boat motor. Owning a diesel truck you get used to getting fucked on the cost of fuel, filters and for some reason if you go to a quick lube it will cost $100 for a simple oil change, but doing it yourself even if the engine takes nearly 2 gallons of oil it is 1/3 the cost of a monkeylube.

[MaxChlan]

I second the use of Shell Rotella. My cousin and friends run Shell Rotella 10w30 in their RB-swapped 240sxs, and I used Triple-T 10w30 before it got hard to find. I now run T5 10w30 all year round without issues. I change the oil every 3k miles because the build is original, and it burns a varying amount depending on how cold it gets.