I probably shouldn't talk with my link to a "budget" rear sight tool. But with $3,500 into my 1981 vintage H&K 91, I think its OK to spend a little bit of $$ to get a proper rear sight tool.
And for pity's sake anyone running a real H&K MP5 please spend the money on a real rear sight tool - no field expedients here - please - your gun will thank you for it.