I removed the rear bumper from my 240Z to replace the rubber trim pieces on the bumper ends and over riders.  The 50 years of rust seem to have bonded the over rider attachment nuts to the studs.  I've soaked them with multiple applications of PB Blaster for a few days, and they're still rusted on tight.  

Any suggestions for a better brand of penetrating oil?  I did the front bumper rubber a couple months ago and all went much easier.

 

PB always got me unstuck. I’ve also used a mix of ATF and PB, and let it sit for extended periods of time.
 

Some people really like Kroil, I’ve never used it (can’t seem to find it locally)…

Kroil.   Amazon

Kroil is one of the best commercially available penetrating oils. You can get it as a spray or liquid in a can.

Thanks for the recommendations.  I've seen good reviews on Kroil.  I wonder how different the various brands are - PB Blaster, Kroil. Lucas, WD40. others.

Tried them all. Kroil by far the best in my opinion.

50% ATF 50% Acetone

Don't forget Gibbs.  Just another highly useful product.  Pricey though.

I like this one:

but also get great results with PB Blaster.  

I suspect that all the "major" brands do about the same job, maybe variance in time to work or something.

My one attempt to use the ATF and acetone potion was a dismal failure, but then I don't follow instructions well or have much patience.

My only real advice here is 1. Don't bother with WD40, and 2, be patient and use several clean it, soak it and let it work sessions. Again the patience thing usually bites me on that last one...

 

1 hour ago, zKars said:

 

My only real advice here is 1. Don't bother with WD40, and 2, be patient and use several clean it, soak it and let it work sessions. Again the patience thing usually bites me on that last one...

 

The "patience thing" seems to be working.  After four days, I finally got one of the over riders detached from the bumper.  Consumed one can of PB Blaster, some WD40, some Lucas penetrating oil spray recommended by a friend who uses it on his old Lotus and Corvette, a brass wire detail brush for cleaning bolt threads, and bought a set of offset box wrenches at the "disposable" tool store Harbor Freight for better leverage,

The second over rider is soaking and I'll try again tomorrow morning around 6:30 AM while the temperature is still under 100º.  It's not a hobby, it's an adventure! 😎

Patience, like caffine in Sprite, never had it, ha ha ha, never will.

 

One tip I have used for breaking loose bolts: Before you try to loosen it, torque it slightly tighter. This may give you a little wiggle room to get it started turning the correct direction to loosen it.

This actually worked for one screw when I was trying to remove the grille. 

Don't forget that heat can be your friend. Sometimes a heat gun is enough.