WD60EZRX speed dipping

Hi,

I posted this on hddoracle and a few users said this is a weak head issue, I'm waiting for my reply to be approved by the admin and I think maybe it never will without me contacting them via their ebay account again so I'll post here instead.

About a year ago I noticed the speed on my drive was dipping down to ~10MB/s. Since then it's not got any better/worse and there are no SMART errors. As far as I can tell no data loss and a clone was just succesful. I've now replaced the drive with a new one but am curious what's wrong with it and if there are any possible solutions?

Here you can see during the clone on the bits where the speed would drop it would be ~10MB/s for 32 seconds then it would shoot up to max read speed for 8 seconds and repeat. Like clockwork.

This is from 5 years ago when the drive was new and working fine.

I've tested the drive connected directly to the motherboard and in an external USB dock with the same results. Also tested it unmounted to rule out drive access during the test.

Any explaination or solution welcome, seems a really strange one.

Thanks.

If the problem is a weak head as suggested would it be possible as a HDD repair novice to repair or disable it myself with the guidence from your good selves or am I out of luck and it's EOL for this drive?