As above i would replace the stem seals first but as mentioned the dipstick popping out is usually a sign of excessive crankcase pressure caused by worn rings.

You can replace them without removing the head and the tool is available from most motor accessory stores. Make sure you have the piston for the cylinder you are working on at TDC so if a valve does slip the piston will stop it.

A couple of pics in my rebuild thread may be useful to you so you know what to expect once the rocker cover is off....

https://passionford.com/forum/viewtopic.php?t=285199