Hey, another old-time painter.
My favorite sealer was Velva-Seal. Used to be a solvent based undercoater and then it went water-based. I hate water-based paints. Like painting with water color.
But nonetheless, it gives a uniform base for the finish coat and seals all those pores and sanding scratches. Paint should go on smooth so color sanding and polishing is just a surface finish for a glass look.
Nobody paints like this any more.
Dupont's chroma-color/chroma-clear system is a good voc compliant product, I may have mentioned this, but it's about five times the cost. Nice hard durable finish though.
I'm not a good enough painter to get by with a thin clear coat to polish, so my single stage paints get polished pretty good. Yes, I have rubbed thru a finish coat getting it to shine.
Painting is an art and a fun endeavor for the patient individual that is willing to learn the finer details. Very satisfying when you can take your picture in your reflection.
The industry keeps marching on in technology and it's hard to keep up unless you're a pro. But they do publish good technical information to help you get with the new finishes with success.
It's very hard to duplicate the finish MB put on their cars. Porsche too. I had a 76 911 in or around 86 that I bought from a guy that had broken his arm playing tennis or racquet ball. It was pretty oxidized and looking worn. But a good buff out brought out a finish that was as stunning as new. Learning paint polishing techniques is almost as important as laying down paint. That's a whole 'nother topic altogether.
EDIT: And while you can't buy centari in cali anymore, you
can have a friend or relative buy it in AZ and ship it to you. And no one with a commercial paint booth will let you shoot it because CARB comes around and takes samples off their exhaust fan screens. If they find banned paints they fine them big-time or shut them down. But it shoots great in your garage.
EDIT2: BTW, it's spelled urethane. An acrylic enamel like centari with a cross-linker harder chemically sets up just like a two part paint, or a urethane enamel.
Mar-hyde makes a great high gloss hardener that is half the cost of duponts hardener, a must for acrylic enamel to make it super durable and fuel proof.
A lot of people used to shoot hobby cars with Dupont Imron which
is a linear polyurethane finish, was developed for the aircraft industry. But it can't be polished and is extremely hard like epoxy. Also outlawed by california air resources board. Funny, a rusty car will literally rust out underneath Imron and leave the shell in tact. They get to be like paper mache.