After cistern refill outflow into toilet bowl continues to dribble in - and you can see a slight flow into the bowl and every so often we hear the cistern refilling a small amount to compensate.

There are bolts attaching the tank to the bowl check to see if they are correvtly tightened after you check to see if the gasket is properly seated.

Hi Juan
Unfortunately we can't see what you can see. The problem must be right in front of you but you are missing it. Eg Parts / Seals in backwards.
If you can't figure it out and it's that urgent then call a plumber.
Good Luck

With lid removed, look down into it and remove and replace the black rubber thing in the center. This is the flush valve and is worn to the point where is no longer provides a tight seal allowing water to pass and run into bowl. Also, could be something underneath it not allowing it to seat properly.

toilet will need syphon replacing. the lid should lift of the cistern, some have the push buttons screwed down to the syphon and to remove them just turn the ring around them anti-clockwise.

Fixing a leaky toilet is actually rather simple, requiring few tools and just a little time and effort. In looking at Caroma toilets on Google, they appear to be just a standard type of unit, and should present few if any problems for yourself or any handyman of modest skill.

If it is leaking around the base of the toilet - where the toilet sits on the floor, the repair item is a simple wax seal. Here is a tutorial to effect this repair: Replace Toilet Wax Ring. The wax ring is very inexpensive, usually $5 to $10 USD.

If the water is leaking from between the tank (cistern) and the toilet bowl, the job is even easier, as it does not require lifting and moving the entire toilet. A good tutorial for that repair is here: How to Replace Tank to Bowl Gasket . The gaskets, new nuts, bolts and rubber seals come in a kit and also cost only $5 to $10 USD.

I am sorry to hear your Plumber insisted you buy an entire new toilet, but do remember he is in the business of making money!

if you flush and the water continues to run into the bowl the it is the flush washer that needs repalcing
If that water shuts off and the cistern fills and then continues so that it flows down the over flow pipe into the bowl the it is the water inlet control washer that needs replacing

IT SEEMS TO ME THAT THE BALL-**** (FLOAT SWITCH) IN THE CISTERN IS SET TOO HIGH UP. THERE ARE MANY DIFFERENT MODELS BUT ALL SHOULD BE EASILY ADJUSTED. HAVE A LOOK INSIDE THE CISTERN AND ADJUST THE FLOAT SO THAT THE WATER STOPS AT A LOWER LEVEL. IF THE WATER IS CONTINUOSLY FLOWING INTO THE CISTERN WHEN FULL YOU MIGHT NEED A NEW INLET WASHER

IF YOU PRESS UR BALLCOCK DOWN IN THE CISTERN YOU WILL STOP THE WATER DRIBBLING IN THE TOILET ,JUST VERY SLIGHTLY BEND THE METAL BAR IN THE MIDDLE AND IT WILL STAY DRIP FREE,OR PUT A LITTLE WEIGHT ON THE METAL BAR NEAR THE BALLCOCK...ROB

Based on the phrasing of your question, I'm thinking that the bad noise happens for the first time when the valve opens to start filling (this happens when you first let water into the bowl) and then again when the valve closes (when the cistern is full). Valves sometimes have a high-pitched squealing noise when it takes a long time to open or close this valve. Sometimes, you can make it go away by turning the screw to adjust the height that the ball/float has to be in order to shut off the water (the more horizontal, the longer it takes to shut off the flow, and the longer the noise continues). Sometimes, this is just caused by an aging mechanism and it turns out to be quicker and easier to just replace that part of the toilet (they make replacement kits that are very inexpensive and easy to install).