paint defect on the roof dead center between sunroof and antenna on 1990GT

I am the proud second owner of a  Stone Gray Metallic 1990GT that I purchased about 30 years,  It had spent a lot of time in the New Jersey sun (those wheel well covers had warped and remain so under the rear greenhouse) and then I brought it to my home in the Florida sun.  Maybe 20 years ago I noticed a paint surface defect (maybe the size of a quarter and it  appeared that the paint was raising up) on the roof  in the center just in front of the antenna (this is an aluminum base).  I had a good body shop attend to it.  The explanation was that maybe there was a little dampness in that location on the paint day at the factory.  Well now again if you closely examine this area, you can tell that the paint surface is rippled.  Anybody else with this issue?  Am I being to picky for a 35 year old car?

The roof and rear quarter panels are steel, and the door skins, front fenders and hood are aluminum.

I think you've corrected the issue with corrosion under the paint previously, but perhaps elimination of the rust didn't completely eradicate it and it's bubbled under the paint?  If your car is a show car, perhaps take care of the issue.  If it's a weekend fun car and occassional show car, you can probably take a little time to correct it, but will need to do so before any corrosion becomes worse.  It may be worth having a body and paint shop take a look and advise if it's really just bubbling paint, or if there's corrosion underneath.

As far as being "picky", I don't think so.  I think taking care of your vehicle (whether it's 35 years old or a year old) is a good practice as you rely upon your vehicles to take care of you (start when you need it to start, take you where you want to go...)

Fun car, not show car
Thank you for the advice.
I am curious why this issue would surface at the top of the car and if other owners have had similar issues...maybe the previous owner did something to the car. Water runs downhill. I have a 1993 600SL and I have had issues of rust rot within the doors where water accumulates and does not drain properly, Anyone can figure out why the rust is on the bottom. 928's are weird animals but I love my car and just wish to be a prper custodian...my wife can sell it when I die.

Sadly once rust occurs, if not corrected completely, it will return.  I've had this happen on a few of my cars.  I think a product we have today (POR 15) wasn't available many years ago, and the process of correcting rust was to "grind it out" (or "sand it out" and then primer and paint over it.  

Keeping an eye on it is perfectly fine and a proper custodian.  If it bubbles worse, then take care of it.  But it sounds like your 928 is in fine hands!

LOL regarding your wife selling the 928.  My son has already called dibs and I fear that he'll take the 928 before I kick the bucket!  I jest - he's a fine custodian of a 944 he restored himself, so I am confident that he would care for my 928 very well when I'm no longer able to enjoy it.  He has no interest in my plane however, so I am confident my wife will sell that as soon as i kick the bucket (or before)