The time has come, my 70 F250 leaks like a colander. At 120,000, she doesn't burn oil, but the puddles she leaves everywhere are distressing. It's time for her oil change, and they've quit selling conventional oil. Using synthetic, she might start burning a lot (I've heard it goes right by the rings). I have a new oil pan, and planned to change nearly every gasket. Given that I'm doing that, should I bite the bullet and send the block to be bored? I really don't want to change pistons, that's when a rebuild gets into serious money. Also, it's a 360, if I have it rebuilt, the temptation to stroke to a 390, or 410 or bore to a 406 or 428 might get the best of me. Parts are getting expensive, but prices aren't going down. The 360 has always done the trick. It's not great for towing, but the short stroke wraps out fast. Basically, all the old folks I used to have for advice have died of old age.

 

When I changed to semi synthetic the oil drips were everywhere. What I found out was the conventional oil gunk's up everything. The new oil was cleaning that up which created those leaks. It took about 2 months for the leaks to start to stop. Synthetic oil can and will clean and swell the seals back to normal if they are not too far gone. In the beginning I was for sure I needed to rebuild. Well 6 years later and no leaks to talk about I have done nothing but drive it and when I got my truck running it sat 20 years previously.
What Are the Risks of Switching to Synthetic Oil in Older Cars? | YourMechanic Advice

 

I would not go full synthetic in these engines. Maybe a synthetic blend. The best option is going with Rotella like the big rigs use. It still has zinc in it and it's designed to go longer between changes. Just my 2 cents.

 

X2 on Rotella. The only way to tell if it needs the bore cleaned up is when the heads are off. If it shows taper you should clean up the bore.

 

This is what I've used for the last 6 years.

 

You can still find dino oil if you look.
https://www.quakerstate.com/en_us/pr...l-mileage.html
Fix the gaskets.

Ooops what I posted is not total Dino oil.

 

New pistons or not depends on cylinder bore wear. Which has to be measured with a tool. If an over bore is necessary, you HAVE to buy the appropriate pistons and rings.
As to the synthetic oil, I would go Rotella also or maybe partial synthetic. Not full. I have seen the full ruin piston ring seal to the cylinders.