In this case, should he take his leave before the screenings come to light?

Never leave before getting a new job, i would highly recommend him to go actively find a new job now! Change payslip is a serious, non-disputable offense, even if he can stay, HR wouldnt trust him and this might just come back and haunt him later in the career progression.

change payslip is one of the most serious employment offences. similarly, faking a job you had with a company is also another top serious offence.

salary checks
 

How can you be so certain about your HR not disclosing all these data? Sure, there are some "between you and me" conversations. HR is powerful. They can find out about anything they want.

reference checks are typically more about when you worked at the company, your position, your salary, etc. its not really about how good an employee you were or details about what you actually did.

companies won't really disclose such information due to potential liability issues.

so, if you didn't lie about anything on your application, there's nothing to worry about. its one thing to exaggerate what you did on the job, its another to lie completely about stuff like your grades, whether you really worked at a company, etc.

So far my experience is that only about 1 in 10 checks.

As a professional with 10 yrs exp and 7 job / company changes. Refernce checks are real.
Typically there are 2 kinds. Reference checks with HR to ensure you have no bad records like terminate.. disciplinary issues.
Another is a reference check with your choice of supervisor or past clients. Normally I put in 2 previous supervisor as my referee. HR or headhunter will call both or either and ask many personal qns, esp if you have some promotions in between. Of cos, they always end up well, I would have listed referees which I can trust to deliver good news to my future employer.

Also, to the subject of pay alteration, I have not done it, but have seen a high profile CIO from an MNC did it. in a short stint, I worked with a recruitment company for few mths. The said culprit altered her current salary on resume and when offered the job, refused to show payslip. This move is really shoddy. Most if not all HR will get your last pay slip or tax statement. So cannot siam this. No point over stating. You can however state the dividents/perks to justify your high expected salary though.

But putting in a gross annual salary which include perks, bonus and basic is quite safe. Unless HR ask isit really so high, and ask to see your pay slip, then you can start to itemize your "perks"

I was ever in a job where I was paid good dividends and as such, my basic salary I inflat to show this perk. I simply could not take a minimal increment on top of just basic, as it would mean a pay cut as a whole.

Salary history
 

Is it possible for prospective employer to check salary history through MOM?

background checks
 

MOM, IRAS, CPF, etc, never disclose this information to prospective employer, unless the prospective employer is Singapore government itself.

reality of reference and background checks in Singapore
 

Hi,
read the story of Ramesh Krishnan who got adverse reference checks from AXA. He sood them and got some money.
What is the lesson for Singapore employers?
Do not give out reference checks recklessly.
Be careful of what you speak for you may one day be sood.