My old (8 years) Thinkpad has had: a new battery, a new keyboard (orange juice!), a new screen (upgrade!), new RAM, new HDD and a new charging plug.
All of the above were very simple with just a couple of screws to get the back cover off. No adhesive or force needed. Even the screen simply clipped off. The manual also comes with instructions on how to dismantle the laptop for repairs.
I sourced the OEM parts from eBay.
The only thing I was not able to change was the Wifi card. Apparently it's hard-locked to a specific model in the bios firmware, which I find a bit odd.