Santro Engine Oil Light blinking

Asslam u alaikum.dear fellows my friends santro engine oil light start blinking while driving.we consulted a mecahanic he checked the wiring there was no issue.the wiring was ok.Then we consulted our regular mechanic he said it may me be a faulty oil switch or if not then the oil pump need to be changed.The electrician then changed the oil pressure switch with japanese one (sorry i dont know what that switch is called).Then after changing the blinking was gone.during this problem there was no reduction in acceleration and also we had checked oil level and it was full.(also in jan we had changed engine oil and filter and after that it was driven less then 100km).now after two weeks the blinking had started again.My friend is worried as mechanic told him that engine needs to be opened for oil pump replacement and some other parts has to be replaced and require some expense (recently he has spent almost 15k on gear problems)he is depressed and thinking of selling his car.can you guide what should we do, is this is due to oil pump or some other issue.kindly put some light on it.jazaALLAH khair.