Well, here's a solution, but it will increase search index size. In the ACP, Search settings, change "Min characters indexed by search from the default 3, to 2. Then delete and re-create the phpBB Native fulltext index. You can now find the part number even with a hyphen between the digits.
Depending on how often particular numbers appear, you may have to change the common word threshold setting, or disable it. That will also require re-indexing.
EDIT - Note that the search will find all occurrences in which both the two numbers appear, like
63526 other stuff 50. But this still should work as the non-relevant results are easily spotted.
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