Can anyone help?

We moved into our house about seven years ago, just after getting a new
oil-fired CH system installed.

Until last year all was well, then our L/R radiator spring a leak. We
replaced it but since then another three have done likewise, all about
2/3 months apart.

We had inhibitor added after the second but it doesn't seem to have
slowed the leaks down.

Can anyone please advise on a cause/fix. From reading previous posts we
may need to replace all the rads and completely flush out the system,
or will it be even more complicated/expensive than that?

Thanks,
George