Hitachi head swap problem

Hi there hdd guru. here some question..

I got Hitachi-IBM 2.5" harddisk (Clicking sound) which I confirm need a head swap.
Model : IC25N020ATMR04-00 4200RPM
made in Thailand APR-04
P/N : 08K0632 MLC : H69555

change with this head :
Model : IC25N020ATMR04-00 4200RPM
made in Thailand OCT-03
P/N : 08K0851 MLC : H69421

problem :
1. After change the head, the clicking harddisk (with good head) still clicking. when I change back the head, the head still good in the original harddisk.
2. What make this change not compatible? cause I see the model and the country are same
3. What criteria should we follow in order to change Hitachi head..

thanks

update for headswap

the head swap perform successfully. but get many UNC ERR when scan with MHDD.
the proses is :
1. Change the head from good harddisk to bad harddisk ( the one to recover the data )
2. write NVRAM to donor PCB
3. Mount this good PCB to bad harddisk

I'm doing this ( step 2 & 3 ) because I don't have exact match donor good harddisk .. can be see below, the P/N and MLC not same, so hopefully with change the pcb also can make me to retrieve the data..

my question is :
1. How Important this P/N code and MLC code in head swap ?
2. What make MHDD scan a lot of UNC. I also try to clone using COPYR, but really slow and produce a lot of ERR.
3. What I'm missing ??

Thanks
regards
Tony

I have performed hundreds of headswaps on ATMR disks and generally I match only the model, but matching the MLC also will be much better. If you repeat this head swap then use a match with same MLC. If there is no change then I suspect you have some service area damage or surface damage.