andy everett wrote:

I have home heating oil tank (in the basement) that is original to a
home built in the 50's. Is there a rule of thumb as to when to replace
them? I also wonder if when tanks fail do they usually develop small
leaks or do they "split" open and release a tank of oil all at once?

Thank you for any advice!

More likely it will develop pinholing along the bottom
since that's where the sludge and water accumulate.
A good backup is a long plastic tray (mud mixing)
under the tank.

If your home insurer does inspections or asks for
documentation, that may force a replacement.

OTOH, it might last another 50 yrs...

Jim