If you're not in a hurry to spend too much on the car, get your hands on a can of BARDAHL engine treatment, pour it in during the next oil change. For an old car, SAE20W50 is suffice. No surprises. Check tyre pressure, make sure it stay above 30, below 40PSi on all time. Ayam usually 34PSi all round, if go long distance belakang will go 32PSi. Drive sensually, FC can cincai beat 12km/l. Try to pay attention to engine sound, whilst going up hill purposely use the wrong gear, like 4th? Try to ehar whether there's klicking sound from the engine. If yes, then need to send workshop retard your ignition timing abit. If you're good at it, release the lug nut that holds the distributor then gradually knock it counter clockwise a lil bit, tighten it back and you're retarded your engine ignition has been retarded.

Have fun playing with the fun ORION

The cheapest oberhol I did was about RM600. Took me 24 hours to get the job done That was my 1st ORION 8Valve 1986 GaGa. Nowadays, it should be around RM1000 depending on which magician u go to.

Brake fluid flush, yes pls go ahead. Transmission fluid, change will do. DO NOT FLUSH. You wouldn't know what kind of rubbish flushing agent your magician gonna put in, later housing leak oil lar, driveshaft leak oil lar, flywheel leak oil lar, then u not only need to oberhol injin, gebox oso need oberhol liao

full overhaul these days are in the 1-2k range, depending on part (ori or oem etc) and labor and whether mechanic is honest/competent or not (eg: some parts no need to change, mech says change anyways)

in addition to what bro david mentioned, ok to do transmission flush, however only use reputable products like lubegard ATF flush. not cheap btw
for manual transmission i believe not required as they aren't as sensitive as automatics.

if you're on budget, actually just using cheap proton ATF SP3 at very short intervals (eg: 500 or 1k km) will be sufficient for a "flushing" effect.

your car is auto or manual again?