Is that true that newer Betacam (post 1988-1990) cameras are built with capacitors that when are getting old are leaking on the printed circuit borads and that the inside of 'em is built very tight?

Beware the "capacitor plague": https://en.wikipedia.org/wiki/Capacitor_plague

I have no idea whether or not the Sony Betacams were affected.

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The Sony 8mm camcorders were plagued with failing SMD caps. Not too sure about Betacams, but 8mm, definitely. They even issued a kit of specific capacitors known to fail. I have a CCD-TR81 Hi8 camcorder I bought new for about $1000, with this capacitor problem. Between the caps and the tape guides that would fall apart, not too reliable!

I've spoke to a repairman today. He told me that 20 years old Betacams (I wanted one) had this problem (SMD capacitors) and the '80's ones had bigger one and the iside space was bigger (compomonents not crowded into one each other) so at those cameras it'll we be more easyer to replace the capacitors.
Shees, I do have an 1989 V.H.C.-C. camera ("Panasonic" MC10) and last year was in working order...

There's also a corrosive, and I believe conductive, brown glue problem in pro broadcast gear of that period. Dark days.

I've got a couple DVCPro machines with the capacitor issue. Might as well be doorstops. Fortunately, I no longer rely on them for business.

Chip

But when this problems appeared?

Yes .The classic Sony sick cap syndrome.was there any class action suit over this. It reminds me of the gooey belt and idler syndrome.

"Sony" from the '80's too?
But tube cameras manufactured by "Philips" and "Hitachi" had this nasty probem?

I've heard the 80's sony Betamax consumer camcorders had this issue....Also if you see a surface mount caps in a sony home use Beta deck that is malfunctioning suspect them first.