Can this be a simple repair issue - yes, it MIGHT be
just changing out the flash bulb - almost certainly no
does this usually indicate an internal problem with the unit itself? - almost certainly so.
The charge is stored in a capacitor. Either the capacitor is leaking or otherwise failing, the charging circuit itself is failing, or the circuit which detects "full" is faulty. Any of these MAY be simple, or can be complex. Generally, unless you work with high voltages routinely and know how to do so safely, you shouldn't try to repair this on your own.
"Keeping shooting will do more for the excellence of your photography than most any camera will!" JimmyD, PGS Extraordinaire.