GSM signal poor/weak/no service after water damage. What to change?

Hi,

i had accident with normal water, iphone was turned down, after that cleaned in ultrasonic cleaning station with isopropyl.

Everything is working fine except gsm signal, but sometimes i am able to make calls, send texts etc, but sometimes not. lets say iphone has weak, strong and with no signal modes.

IMEI and ICCID working fine, so i do not expect broken MB.

I have not changed anything till now.

what to change, what to look for?

i have found somewhere that GSM antena is from 3 parts, somebody has some drawing, picture where to look for?

what to clean additionally?

it looks like i have some troubles with shielding/shadow casting, that some connector is not in touch with body or smthing?

pleas for any advice would be thankfull.