A common source of run-on sentences is the inclusion of a parenthetical full sentence at the end of another sentence, for instance,
This is an example (there may be others).
This construction is always wrong. Separate the two sentences, as
This is an example. (There may be others.)
or coordinate or subordinate the two, as
This is an example (though there may be others).
or
This is an example (and there may be others).
The following is not correct:
This is an example (however, there may be others).
“However” is an adverb, not a subordinating conjunction.