what are the symptoms ? radiator water mixes with engine oil or vice versa ? or just giving some air bubbles from radiator and no oil sigh in water ,,,,,,,,,,,,,use original gas kit , dont use silicon as a sealent , i always use the one as i show in pic , its petol based and works good on jans and gaskit , may be you need to reface your engine head because gas kit rarelly leak if you use coolant instead of water and if the head face if all in perfect condition , it sometime happens when engine overheats
https://www.pakwheels.com/forums/performance-modification-tune-up-preventive-maintenance/181721-cultus-engine-body-overhaul-rebuild-22