Here's a definition since you asked for it:
"Political Corruption", as a term by itself, to date is still being
discussed without much headway. There are several schools of
thought on this, continually arguing over the definition in order
to justify their convictions.
I propose then, in order to get started on this topic, without
having to waste time on definitions, that we use the simpler
definitions afforded in dictionaries.
Political, as an adjective to the the noun, Corruption. Corruption
by Politicians so to speak. Then it leaves us to define
Corruption.
Corruption, very simply put is (according to dictionaries) -
"dishonesty and illegal behaviour by people in power or
authority"
Put together, it will be reasonable to define for this argument,
Political Corruption as Dishonest and/or Illegal Behavious by
Politicians who are in authority.
Now, when MM Lee declared that our leaders were incorrupt, it
should be seen in this context:
Singapore Leaders are not guilty of "illegal" behaviour according
to OUR law.
The reason why we dont think this counts for much, is because
Singapore's Law is passed by only one body without a referendum
from the people. The Parliament which is dominated by PAP.
If I was a leader of a country, and I made every kind of law [and
people had no power to complain] to protect my own ambitions and
gains, I would most certainly be incorrupt by definition. There is
no law that I've broken and hence not illegal.
Thus the stated definition of corruption is found lacking.
In view of all this, and addressing your very first motivation to
start this thread, what we are effectively saying is that, there is
nothing to be in awe of such a statement. It doesnt count for
anything.